The gaseous messenger nitric oxide (NO) plays a bewildering number of roles in fundamental processes, such as cell locomotion, differentiation, proliferation and death. Its different and often contrasting roles may depend on its concentration and intracellular site of generation. We describe here a simple system with which to investigate the roles of NO generated at physiological levels in HeLa cells by eNOS transfected under an inducible promoter. This system has allowed us to uncover unexpected signalling circuits between NO and ceramide, involved in the response of cells to apoptotic stimuli. At present, we are using these cells as a tool to investigate the role of NO in migration.