Recent work has demonstrated that a number of signalling events, including cytosolic Ca(2+) rises, cAMP accumulation, activation of protein kinase C, activation of protein tyrosine kinases, and production of ceramide, regulate apoptosis in diverse model systems. However, in some cells these signals promote apoptosis, whereas in others they block the response. This review discusses these observations and proposes explanations for how a given set of signal transduction systems might be involved in multiple cellular responses.