The aim of this study was to investigate the possible time- and dose-dependent cytotoxic effects of cobalt chloride on Vero cells. The cultured cells were incubated with different concentrations of cobalt chloride ranging from 0.5 to 1,000 mu M, and cytotoxicity was determined by 3-(4,5-dimethylthiazol-2-yl)-2, 5-diphenyl tetrazolium bromide (MTT) and resazurin assays. Possible protective effects of vitamin E, coenzyme Q(10), and zinc chloride were also tested in this system. A gradual decrease in cell proliferation was observed at concentrations similar to a parts per thousand yen200 mu M in incubation periods of 24, 48, 72, and 96 h with MTT assay. Exposure of cells to 500 and 1,000 mu M cobalt chloride caused significant decrease in cell survival. A biphasic survival profile of cells was observed at 1-25 mu M concentration range following 96 h of incubation. With resazurin assay, cytotoxicity profile of CoCl2 was found comparable to the results of MTT assay, particularly at high concentrations and long incubation periods. Dose-dependent cytotoxicity was noted following exposure of cells to a parts per thousand yen250 mu M of CoCl2 for 24 h and a parts per thousand yen100 mu M concentrations of CoCl2 for 48-96 h. Pretreatment of cells with ZnCl2 for 4 or 24 h provided significant protection against cobalt chloride-induced cytotoxicity when measured with MTT assay. However, vitamin E or coenzyme Q(10) was not protective. CoCl2 had dose- and time-dependent cytotoxic effects in Vero cells. Preventive effect of ZnCl2 against CoCl2-induced cytotoxicity should be considered in detail to define exact mechanism of toxicity in Vero cells.