After graduate school Saul started his zoo career at the Oklahoma City Zoo. It was 1963 and he was hired, by zoo director Dr. Warren Thomas, as Curator of Primates. When Dr. Thomas went to Omaha Zoo in 1966, as director, he offered Saul the position of General Curator. In 1968 Saul accepted the position of General Curator at Chicago’s Lincoln Park Zoo under director Dr. Lester Fisher. Soon he was promoted to Assistant Director.
In 1975 he was appointed director of the San Francisco Zoo. A main interest was the great apes and he was instrumental in helping to develop and build great ape exhibits in Lincoln Park and San Francisco.