Unable to obtain a graduate research position, she worked as a food quality supervisor at A&P supermarkets, and for a food lab in New York, testing the acidity of pickles and the color of egg yolk going into mayonnaise. Later, she left to work as an assistant to George H. Hitchings at the Burroughs-Wellcome pharmaceutical company in Tuckahoe, New York (now GlaxoSmithKline). Hitchings was using a new way of developing drugs, by imitating natural compounds instead of through trial and error. He believed that if he could trick cancer cells into accepting artificial compounds for growth, they could be destroyed without also destroying normal cells. She began to work with purines, and in 1950, she developed the anti-cancer drugs tioguanine and 6-MP.