The most important private collection of 20th century art ever offered at auction comes up for sale in New York in November. The 115 paintings, drawings, sculptures and prints - carrying a total estimate of US$125 million - were assembled by the late Victor and Sally Ganz, who married in 1942, the same year they acquired their first picture by Picasso.

Passionately interested in contemporary art, Victor and Sally Ganz collected works over a period of some four decades and were frequent lenders to important exhibitions, especially in their native New York. When that city's Museum of Modern Art staged a Picasso retrospective in 1980, for example, they were the largest private lenders to the show.

Their selection of 12 pieces by Picasso is likely to arouse the most interest at the November sale, as some of the work is of exceptional quality. The most important painting of all is Le Reve, dating from 1932 and regarded as one of the artist's finest portraits.

Representing Picasso's mistress, MarieTherese Walter reclining in a chair, this work carries an estimate which is available only on request, an indication of its value.

However, another - and earlier - Picasso, the cubist Femme assise dans un fauteuil (painted in 1913) has an estimate of US$15-$20 million, while the same artist's final version of his Femmes d'Algers series is expected to make $10-$12 million.

Mr and Mrs Ganz also collected art by their American contemporaries, in particular Jasper Johns, Robert Rauschenberg and Frank Stella. Johns, the subject of a major retrospective in New York last year, is represented in the sale by a number of pieces, such as the 1959 White Numbers ($4.5-$5.5 million) and Souvenir 2 from 1964 ($2-$3 million).

Two Rauschenberg paintings incorporate a wide variety of media; 1954/ 55's Red Interior ($3-$4 million), for example, employs oil, velvet, plastic and paper on canvas, while the later Rigger (also $3-$4 million) uses crushed metal objects, wood, fabric and rope on canvas.

Frank Stella was spotted by the collectors early in his career. His Turkish Mambo, painted when the artist was just 24-years-old, has a pre-sale estimate of $6-$8 million but later examples of his work, such as the 1978 Ram Gangra, are expected to go for less; in this case, the estimate is $3-$4 million.

Other artists who are featured in the sale include Sol Lewitt, Richard Tuttle, Brice Marden and Barry le Va, while the most important pieces of sculpture are by Eva Hesse, who died in 1970 at the age of 34.

Her Vinculum I, produced the year before her death, is valued at $400,000-$600,000.

To coincide with the sale, which is scheduled for Monday, November 10th, Christie's will be producing not just a catalogue but also a book called Victor and Sally Ganz: A Life of Collecting, which will document the history of the collection with essays by a number of scholars.