This article is a concise review of up-to-date information and recent discoveries concerning structure, site of action, tissue distribution, biological effects and molecular mechanisms of Bcl-2 family proteins. Particular attention has been focused on the physiological aspect of Bcl-2 protein function with emphasis on animal production and health. Bcl-2-related proteins are the principal regulators of apoptosis, acting through the control of ions (K+, H+, Cl-, Ca2+) and reactive oxygen species fluxes, the release of apoptogenic factors from mitochondria (AIF, cytochrome c) and the activation of the executors of apoptosis (caspases, DNases). The response of Bcl-2 proteins to pro- and anti-apoptotic signals relies on the activation of transcription and translation, phosphorylation, proteolytic cleavage, interactions with Bcl-2-related and other (structurally unrelated) proteins, translocation from the cytosol to intracellular membranes, and formation of permeability transition pores. (C) Inra/Elsevier, Paris.