Cadmium accumulation and cytotoxicity were compared in hepatocytes in primary culture (HPC) or co-cultured (COC) with a rat liver epithelial cell line (RLEC). Cells were exposed for a 15-day period at 0, 0.045, 0.45 and 0.9 mum-Cd in the incubation medium. Cadmium uptake in COC was always linearly Cd dose and time dependent. In contrast, at the two highest doses for RLEC and only at the highest dose for HPC, a plateau in Cd uptake was observed. In viable cells 95% of the intracellular Cd was found in the cytosol, entirely protein bound. In the three types of culture the amount of Cd-metallothionein (MT) complex was proportional to Cd uptake and was in the order: COC > HPC > RLEC. Lactate dehydrogenase release in the medium and the DNA content of the plated cells at the end of exposure accounted for a marked Cd-induced cytotoxic effect in RLEC and a lesser effect in HPC. In contrast, no significant cytolysis was observed in COC. This suggests that although greater Cd accumulation was observed in COC than in HPC and RLEC, the detoxification procedure, dependent on Cd-MT complex formation, was more efficient and longer preserved in COC owing to a greater maintenance of hepatocyte specific functions, as evidenced by albumin secretion. This COC model offers a powerful tool for studying long-term accumulation and cytotoxicity of Cd in vitro at low exposure levels.