Frank McCormick has contributed to our understanding of intracellular signalling pathways related to cell growth and carcinogenesis. In particular, he discovered GAP, a protein regulator of the Ras small GTP-binding protein, which activates the intrinsic GTPase activity of Ras and switches off Ras-induced signals, which can lead to growth or differentiation. The Ras pathway is highly conserved and Ras GAP activities have subsequently been found in all eukaryotes. He has also shown that there are distinct GAP activities for other Ras-related small G proteins. Mutation of a GAP-related protein, NF1, which he showed has Ras GAP activity, is involved in neurofibromatosis type I. He has performed many elegant studies on the regulation of Ras activity and its downstream targets, and is regarded as a world leader in the field of signal transduction.