Primary cell culture was utilized to study the relationships between stress protein induction by zinc in vivo and cadmium toxicity in vitro. Effects of cadmium on cell viability were evaluated by the alamar blue assay, in conjunction with the ultrastructural morphology of cells by transmission electron microscopy. The expression of stress protein gene products was evaluated by35S two-dimensional gel electrophoresis. The results showed cytotoxicity of CdCl2 at and above 129μM (14.55μg cadmium/mL medium) following 4 h of exposure. Prior zinc administration (20 mg zinc/kg, s.c, two daily doses) in vivo significantly protected the cells in vitro as demonstrated by improved cell viability. The 35S labeling of proteins induced by CdCl2exposure clearly demonstrated for the first time that gene product of the 70-kDa family was induced in cultured rat proximal tubule cells which are the target cells for cadmium toxicity in vivo. Zinc in vivo pretreatment of animals induced proteins in the 90-, 70-, and 38-kDa families, which may act together with metallothionein to protect cells against cadmium toxicity. The results also indicate that the protective effect of zinc remains after the cells have been put in culture and thus provides a system in which we can study the changes that occur as a result of zinc exposure that decreases cadmium toxicity.