Bonnie Chajet, a senior vice president at Warburg Realty Partnership, has a formidable Rolodex. That, in a city of networkers and connectors, may not be saying much. But here’s what makes Ms. Chajet’s collection of contacts legendary in New York, where legends are hard-won: She knows them all, several thousand of them, and has personal and professional relationships with them.

“It’s through the connections, the people you know and who know you, that you get the best properties on the market,” Ms. Chajet said. “In the real estate business, it ultimately comes down to trust and integrity.”

Those characteristics have been the hallmark of her career. She and her partner at Warburg, Ronnie Lane, are celebrating 30 years in the business. In fact, theirs has been the longest running and most successful real estate partnership in New York. Their careers are case studies of how to execute complicated residential property deals in record time, and to the satisfaction of seller and buyer alike.

And it has made them into models for a new generation of real estate brokers – which includes one of Ms. Chajet’s two daughters, Lisa, who’s also at Warburg.

“In this business, the most important thing is your reputation,” the elder Ms. Chajet said. “Unless you build that reputation, you’re not going to be successful. And you build that reputation deal by deal, relationship by relationship.”

In her early years in real estate, she built her reputation door by door. She would walk up and down the avenues of the Upper East Side and the Upper West Side in Manhattan, befriending doormen. They became invaluable sources of information about apartments that were about to go on the market. Once, when she and her husband Clive – who’s well-known in his own right as a creator of corporate and brand identities – were strolling down Park Avenue, so many doormen waved to her that Mr. Chajet asked his wife if there was anyone in Manhattan who didn’t know her.

Ms. Chajet’s efforts to cultivate sources such as doormen yielded dividends early in her career. She was able to obtain a 10-room Park Avenue apartment for a customer in the mid-1970s for $78,000. A couple of years ago, he sold that property for $3.5 million (although not through Ms. Chajet).

Until recently, Ms. Chajet and Ms. Lane made between 40 and 50 deals a year. In 2003, they undertook 62 transactions, with prices generally ranging between $2 million to $4 million. But residential real estate values – particularly on Manhattan’s Upper East and West Sides – have skyrocketed recently to the point where the average price of a home is more than $1 million, and residential property is fetching more than $800 a square foot.

(The value of all property in New York is $616 billion, according to the city’s Department of Finance. Jonathan Miller, head of Miller Samuel, a top real estate appraisal firm, said yesterday that the value of residential property transactions in Manhattan in 2004 was more than $10 billion.)

“The market value of apartments has gone up so much that we do fewer deals now, perhaps around 20 a year,” Ms. Chajet said.

According to standard real estate literature, market value is generally defined as the price a willing buyer would pay a willing seller for a property in its present condition, with neither buyer nor seller under pressure to act due to such issues as job transfers, the death of a family member, or divorce. A market-value sale also is known as an arm’s length transaction.

Several factors such as location and amenities can affect a residential property’s market value, Ms. Chajet said. But the law of supply and demand is ineluctable. “There’s always a short supply of quality products,” she said.

That means she and Ms. Lane – who are among eight partners at Warburg, a 109-year-old company headed by Frederick Warburg Peters – must continuously be on the lookout for properties that may come on the market. One measure of her success in winning clients’ loyalty is that Ms. Chajet has sold apartments for three generations of 10 families.

“I find it very challenging to find the right places,” Ms. Chajet said. “And I get enormous satisfaction from matching sellers and buyers. Fortunately, I no longer have to walk door to door to find available places. I have the access now that I didn’t 30 years ago. Technology – computers – has made the job somewhat easier.”

Easier perhaps, but no less complicated than when Ms. Chajet got into the business in 1975. Previously she had worked as a personnel manager with J. Walter Thompson, the advertising company. (It was acquired in 1987 by WPP, the communications conglomerate.) She had two young daughters, Lisa and Lori, and naturally wanted to devote more time to raising them. She met Ronnie Lane by coincidence during a summer break; Ms. Lane, who had two young sons – Craig and Drew – was, like Ms. Chajet, studying for a real estate licensing exam.

Both women hit it off, Ms. Chajet said, and went to work at Lansco, a commercial brokerage. But they decided to move into residential properties because, as Ms. Chajet put it, “We each had young children, and residential real estate was a way to not do it full time and split the load.”

Ms. Lane has been famously quoted as saying of their partnership: “We’re both mildly aggressive and have similar-type lifestyles, and we both are motivated to the same degree.”

That motivation and assertiveness are needed because closing deals is a complicated business. “You need to sell a property twice – once to the buyer, and again to the co-op board, whose members need to be convinced about the credentials of that buyer,” Ms. Chajet said. “And how do I assess a person? Well, call it my ‘real estate gene.’ “

But even before due diligence about a buyer’s credentials is undertaken, the property needs to be advertised and marketed. Under the rules of the Real Estate Board of New York, a broker must make information available about a property he’s been asked to sell to other brokers within 72 hours. This is usually done through the Internet.

A seller, of course, can choose to give “exclusive” selling rights to a specific broker. Sometimes, Ms. Chajet said, co-deals occur, when a broker from a competing company is also selling the same property. Such arrangements, she said, are mostly cordial, although occasionally she has encountered “an unethical broker.” After all, the residential real estate world isn’t that big. Besides Warburg, there’s Stribling and Associates, another independent firm that also specializes in luxury apartments; and there are the giants, such as Prudential Douglas Elliman, and the Corcoran Group.

As for convincing co-op board members – and ones in Manhattan are notoriously finicky – that’s where Ms. Chajet’s huge Rolodex again comes into play. As her husband would say, she knows just about everybody.

“One reason that I think I’ve attained success is that I’m more concerned about developing and nurturing relationships with my clients, and with colleagues in the field,” Ms. Chajet said. “It’s these relationships that truly matter. The deals will always come your way if you pay enough attention to people.”