 Upon completion of his thesis in 1950, Janowitz returned to the Gastrointestinal Physiology Laboratory as full time researcher.While at the lab, he worked under Franklin Hollander, who at that time was a renowned gastroenterologist after publishing his investigations into gastrointestinal electrolyte metabolism.Janowitz became a private practitioner in 1952 and worked closely with Burrill Bernard Crohn at Mount Sinai Hospital in Manhattan, New York.