Provided here is an up to date account of how high pressures affect cellularprocesses in microorganisms and in eukaryotic cells. Topics include membranetransport, cell activation, the excitable properties of cells, muscular contraction, with particular emphasis on cardiac muscle, and the role of pressure in the physiology of cartilage in load bearing joints. Additionally there are thorough reviews of the effects of pressure on fish and on the central nervous system of mammals, including man.