Exposure of plants to elevated temperatures induces a complex set of changes that enable plants to adapt following heat stress. In order to test the effect of Ca2+ on heat shock-induced changes in cell protein synthesis the incorporation of [ S]methionine into protein was studied in cultured sugar beet (Beta vulgaris L.) cells incubated in media containing different calcium concentrations. Heat shock inhibited the synthesis of non-heat shock proteins (non-HSPs) and promoted the synthesis of a set of HSPs, typical of plants. The synthesis of non-HSPs was greatly inhibited by external Ca2+ removal by treatment of the cells with ethylene glycol-bis(β-aminoethylether)-N,N,N′,N′-tetraacetic acid. In contrast, extracellular Ca2+ appeared not to be strictly required for the de novo production of HSPs, but this cation exerted different effects on the synthesis of individual HSPs. Cell injury increased if the cells were exposed simultaneously to high temperature and Ca2+-deficient medium. Recovery of HSP synthesis and reduced cell injury were observed after addition of exogenous calcium to Ca2+-depleted cells. These findings are consistent with a Ca2+ requirement for the survival of the cells under heat shock, and likely for the development of cell thermotolerance.