Then, in 1948, when Janis was 52 years old, he and Harriet opened the Sidney Janis Gallery which was located at 15 E. 57th Street in Manhattan sharing the fourth floor with the Betty Parsons Gallery. The gallery soon acquired a strong reputation by mounting scholarly, curated exhibitions of Léger, Mondrian, the Fauves, the Futurists, and de Stijl artists. In the 1950s, the gallery became a powerhouse of contemporary avant-garde art. In 1952, Janis gave Jackson Pollock the first of three solo shows. Also in this decade, the gallery represented Arshile Gorky, Willem de Kooning, Franz Kline, Mark Rothko, Robert Motherwell, Phillip Guston, Adolph Gottlieb, William Baziotes, and Josef Albers. In addition to his promotion of the Abstract Expressionists, Janis become the first blue chip gallery to show Pop art. In the fall of 1962 he organized the groundbreaking exhibition, the "International Exhibition of the New Realists", a survey of contemporary Pop art and the seemingly related Nouveau Réalisme movement. The exhibition was located in a temporary rented storefront at 19 W. 57th Street. Robert Motherwell, Mark Rothko, Phillip Guston and Adolph Gottlieb left the gallery as a protest. The Sidney Janis Gallery soon became a leading exhibitor and dealer in Pop art, representing Claes Oldenburg, Jim Dine, Tom Wesselmann, George Segal, Öyvind Fahlström, and Marisol.