Walking into Wildenstein & Co. on East 64th Street off Fifth Avenue, a visitor could imagine being magically transported to a mansion in the Eighth Arrondissement. This is an appropriate mood in which to take in Wildenstein’s current exhibition: the largest exhibition of Monet paintings in New York in 30 years.

The gallery’s director, Guy Wildenstein, decided to mount the exhibition, which includes three never-before-exhibited and several rarely exhibited paintings, to honor two people who contributed to Monet’s reputation and legacy. They were his father, Daniel Wildenstein, who wrote the two-volume catalogue raisonné and who died in 2001, and Katia Granoff, a Russian émigré art dealer who created a market for Monet’s late work in the 1950s and ’60s, when it was significantly undervalued, and who died in 1989.

The show includes loans from 18 institutions and as many private collections. An early painting of Monet’s father, “Adolphe Monet in the Garden of ‘Le Coteau’ at Saint-Adresse” (1867), with beautiful dappled light and bright colors, has never been shown before and never been reproduced in color. The painting is from the same group of family pictures as the Metropolitan Museum of Art’s “The Terrace at Saint-Adresse,” which also shows Monet’s aunt and cousin.

Mr. Wildenstein and the curator of the exhibition, Joseph Baillio, tried to secure from the Hermitage Museum in St. Petersburg the pair to the painting of Adolphe, “Young Woman with a Parasol in the Garden of ‘Le Coteau,'” which depicts Monet’s cousin. They even convinced the owners of “Adolphe” to offer to loan their painting to the Hermitage in exchange — but the Hermitage wouldn’t agree to the arrangement. “Maybe if we had been a museum,” Mr. Wildenstein said.

The two other never-before-exhibited works are “Through the Trees, Île de La Grande Jatte” (1878), which Monet painted standing on the banks of the Grande Jatte and looking, through dense, green foliage, across the Seine at the village of Courbevoie; and “Villas at Bordighera” (1884), painted on the Italian Riviera.

The exhibition includes a room on the first floor of enlarged photographs of Monet, and numerous letters from Monet to the love of his life, his second wife, Alice Hoschedé. Alice initially was married to one of Monet’s first patrons, Ernest Hoschedé. After Hoschedé went bankrupt in 1877, the two families moved in together in a house in Vétheuil, and Hoschedé spent most of his time in Paris. Monet’s first wife, Camille, died in 1879. Ernest Hoschedé tormented the artist by surviving until 1891, at which point Alice finally agreed to marry Monet.

The translated letters, which date from the early 1880s, show Monet deep in the moodiness (often, crankiness) of the frustrated lover — and, of course, also the practicing artist. Writing to Alice in February, 1883 from Étretat on the Normandy Coast, Monet complains for several lines about the horrible weather, then adds: “I am very restless and in a foul mood, therefore your tiny letter written in such haste has done nothing to soothe my feelings.” A few days later, after some blowup between them, he writes: “Forgive me for having tormented you with the wire I sent you, but I have been in such a state the past days that I am overwhelmed and like a madman.”

From Bordighera in February 1884, he writes that he has had an awful night: “continuous nightmares, imagining all my paintings with false colors, then taking them to Paris where everybody admitted to me that they didn’t understand a thing about them.” (Looking at these paintings, with their almost psychedelic colors, one can see why he might have been nervous about their reception.)

Mr. Baillio, a friendly, talkative man with a ring of gray hair, has been working on the exhibition for two and a half years. When he started, “he had long hair, black, flowing,” Mr. Wildenstein teased his colleague yesterday morning. “He lost all of it trying to get these pictures!”

Tickets to the exhibition, which cost $10, will benefit the Breast Cancer Research Foundation.