We have compared response of renal mesangial cells to different does of cadmium. The effect of cadmium was assessed by measuring the growth rate of an homogeneous rat renal cell line. The cells grown in the presence of 10-6 MCd exhibited a 37+/- 6% mortality rate within 24 h. When the cells were first placed in the presence of 10-15 or 10-20 MCdCl2 for 24, 48, 72 and 98 hours respectively and then placed in the presence of 10-6 MCdCl2, the toxic effect initially observed with this concentration was significantly reduced. This decrease in Cd cytotoxicity was also dependent on the pretreatment time. The maximum resistance effect was obtained after 72 hours of pretreatment, a 45=/-6% increase in survival rate was observed. However, 96 hours pretreatment did not increase the protective effects. In conclusion renal mesangial cells alone may exhibit a transient protective mechanism against a toxic dose of cadmium itself at doses as low as 10-15 and 10-20 M. The induction of metallothionein is likely to be involved.