Donald F. Steiner is known for his discoveries on proinsulin, the precursor of insulin which is a hormone that helps the body control the use of sugar. He found that insulin is synthesized from a larger precursor protein in the beta cells of the pancreas and this led the way to elucidation of how the islet cells function, and how peptide hormones, in general, are synthesized and metabolized. He and his colleagues have also devised methods for measuring insulin and its precursors in human serum.
In 1984/5, he was awarded the Wolf Prize in Medicine for "his discoveries concerning the bio-synthesis and processing of insulin which have had profound implications for basic biology and clinical medicine". He also received the Canada Gairdner International Award in 1971, the Banting Medal for Scientific Achievement from the American Diabetes Association in 1976, and the Ernst Oppenheimer Award for the Endocrine Society in 1970.