The purpose of this study was to compare cytotoxicity tests for industrial/municipal wastewaters using two different cell systems: rainbow trout hepatocytes and gonadal fibroblasts. They were exposed to concentrations of industrial/municipal wastewaters for 48 h at 15 degrees C. In addition, wastewater toxicity was evaluated concurrently with the 96-h rainbow trout acute lethality bioassay. Hepatocyte viability was assayed with the propidium iodide (PI) exclusion and neutral red (NR) uptake inhibition tests, while gonadal fibroblast viability was assayed with the NR uptake test. The results show that hepatocyte viability measurement by the PI exclusion test and NR uptake are in agreement with complex mixture exposures. Moreover, cytotoxicity was correlated with trout mortality for most of the effluents (80%). Although a low correlation was found between the trout fibroblast and the hepatocyte NR uptake assays, the NR uptake assay using gonadal fibroblasts was correlated with trout mortality, but in only 60% of the samples tested. Hepatocyte cytotoxicity data, whether determined by the PI exclusion test or the NR uptake test, appeared to be more strongly associated with trout toxicity than did the rainbow trout gonadal fibroblasts, in the case of complex environmental mixtures.