Abstracr , Many metals act on biological systems at low concentrations and recent epidemiological and experimental research indicates that toxic effects of certain metals occur at levels only marginally higher than those found in healthy subjects. Despite a large number of studies describing metal cytotoxicity, the molecular mechanisms involved are still poorly understood. However, it now seems evident that several metals can interact with enzyme functional groups and that proteins involved in signal transduction, including CaZ+ channels and pumps, may be especially sensitive to this interaction. Impairment of the ability of cells to adequately respond to the stimulation by hormones and growth factors may result in the loss of important cell functions or activation of mechanisms that compromise cell survival. In the following sections we will briefly describe the effects of various metals on cell signalling and present our recent findings on the mechanism by which inorganic mercury affects signal transduction. Barnes , D. S. : Cells without growth factor commit suicide. Science l988,242,1510-1511. kinetic analysis of the effect of adrenalin on calcium distribution in isolated rat liver parenchymal cells. J. Physiol. 1981,312,29-55. Bellomo, G., H. Thor & S. Orrenius: Alterations in inositol phosphate production during oxidative stress in isolated hepatocytes. J. Biol. Chem. 1987,262,1530-1534. Berlin, M., J. Carlson & T. Norseth: Dose-dependence of methylmer-cury metabolism. A study of distribution: biotransformation and excretion in squirrel monkey. Arch. Environ. Health 1975, 30, Berridge, M. J.: Inositol trisphosphate and diacylglycerol: two interacting second messengers. Annu. Rev. Biochem. 1987,56,159-193. Berridge, M. J.: Calcium oscillation. J. Bid. Chem. 1991, 265, Bingham-Smith, J., S. D. Dwyer & L. Smith: Cadmium evokes inosi-to1 polyphosphate formation and calcium mobilization. J. Biol. Chem. 1989,264,7115-7118. Bondy, S. C. & A. K. Agrawal: The inhibition ofcerebral high affinity receptor sites by lead and mercury compounds. Arch. Toxicol. Bottestein, J. E.: Growth and differentiation of neural cells in defined media. In: Cell culture in the neurosciences.: Evidence for the involvement of dithiol groups in mitochondria1 calcium transport: studies with cadmium. Arch. Biochem. Biophys. 1985, 242, 493-497. 307-313. 9583-9586. 1980,46,249-256. 1976,5337-349.