In the annals of real estate, 2005 may be recalled as the year that the leading property-owning families of New York decided to sell residential rental buildings. The sellers – whose companies were established in the early 20th century – include Rudin Management, Jack Resnick & Sons, Rose Associates, and the estate of Sarah Korein.

In 1931, Korein purchased her first building, a six-story walk-up apartment house in the Flatbush section of Brooklyn. At the time of her death in 1998, Korein owned the Delmonico Hotel at 502 Park Ave. and residential rental towers at 220 and 240 Central Park South. Last month, her estate agreed to sell a 124-unit, 150,000-square-foot residential building at 220 Central Park South with additional air rights for approximately $132 million to the Clarrett Group.

Jack Resnick opened his real estate brokerage in the Bronx in 1928. Jack Resnick & Sons has become one of the largest owners of office properties in New York City. The company is building a 257-unit residential condominium tower at 200 Chambers St. In 1998, the company completed a 41-story, 550-unit rental tower called the Gershwin at 250 W. 50th St. The tower was financed with bonds issued by the New York State Housing Finance Agency under the 80/20 program, which stipulates that 20% of the units must be reserved for low-income tenants earning no more than 80% of the local median income. The tower is on the market and could sell for more than $410 million.

In the 1970s, Leonard Adell, a clothing manufacturer, began assembling parcels in the manufacturing and flowershop district on Sixth Avenue between 23rd and 30th streets. In 1995, 24th to 31st streets along Sixth were rezoned for residential. Last week, Adellco contracted to sell the Aston, a 38-story, 266-unit, 80/20 apartment tower with 12,000 square feet of retail space at 800 Sixth Ave. that was built in 2003 for $195 million to a Colorado based REIT, Archstone-Smith.

In 1905, Louis Rudinsky, a young immigrant from Belorussia with a dry goods store on the Lower East Side, was approached by his attorney with an opportunity to purchase a four-story brownstone at 153 E. 54th St. In 1964, Samuel Rudin, the son of Louis Rudinsky, built a 32-story office building on the site once occupied by a brownstone at 641 Lexington Ave. On his deathbed, Louis Rudinsky commanded his son Samuel to never sell the property.

In March, Rudin Management sold the land under a cooperative apartment building at 2 Fifth Ave. to the cooperative for $29.25 million. Rudin Management is a firm that manages the Rudin family’s holdings, which include 14 office buildings and 22 apartment houses. Last month, it announced plans to sell two residential rental towers at 30 and 40 Park Avenue in Murray Hill.

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In 1928, David Rose, founder of Rose Associates, began construction of a six story apartment building in the city. Today the company operates as a developer and manager of over 30 million square feet of commercial space. In April, the company sold the Sheffield, a 50-story rental apartment building, for $418 million to a partnership of Yair Levy, Serge Hoyda, and Kent Swig. Later this month, the state Housing Finance Agency is expected to approve 80/20 bond financing for a rental apartment building with more than 400 units that Rose intends to build on Avenue of the Americas between 25th and 26th streets.

Last month, Mr. Swig’s Swig Equities signed a contract to pay $260 million for a former office building at 25 Broad St. that had been converted into 347 residential apartments.

In 1975, Donald Trump optioned the 75-acre Penn Yards site, which stretches from 59th to 72nd streets. In 1985, Mr. Trump purchased the site for $82 million in partnership with Abraham Hirschfield. In June, a partnership made up of Hudson Waterfront Associates, a group of Hong Kong investors, and Donald Trump entered into a contract to sell three residential rental apartment buildings and a 5-acre parcel between 59th and 62nd streets to Excell Development and the Carlyle Group for $1.8 billion. Two weeks ago, the purchasers resold the 1,325-unit residential rental apartments, 40,000 square feet of retail space, and 424 parking spaces to Equity Residential Properties Trust for $816 million.

Last October, Equity paid about $100 million to World Wide Holdings for the landmarked 71 Broadway, which was converted into a residential rental building in the mid-1990s. Last month, a joint venture of World Wide Holdings and Lubert-Adler contracted to sell a former office building at 88 Greenwich St. that had been converted into a 458-unit residential rental building for $195 million to Thorwood Real Estate.

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Insurance companies have developed and operated a number of apartment houses in the city. Between 1939 and 1949, Metropolitan Life built the 12,271-unit Parkchester apartments in the South Bronx, the 12,000-unit Peter Cooper Village-Stuyvesant Town in Manhattan, and the 1,250-unit Riverton Apartments – one of the premier middle-class apartment complexes in Harlem – which is between Fifth Avenue and Harlem River Drive from 135th to 138th streets. It’s expected to be sold next month for more than $140 million.

In the 1950s, New York Life built Manhattan House, a 582-unit apartment house at 200 E. 66th St. The building is being marketed for sale and is expected to fetch close to $525 million. The Riverton and Manhattan House are expected to be converted into residential condominiums.

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Everyone is questioning if and when the real estate marketplace is going to have an adjustment. All of a sudden, this year some of the sellers cashing in on the record prices are established real estate families and development companies. Timing is everything in business and in real estate. Only time will tell who is better off, the buyer or the seller.

Mr. Stoler is a television broadcaster and vice president at First American Title Insurance Company of New York. He can be reached at mstoler@firstam.com.