The influence of interactions of cadmium, zinc, lead, and mercury on the growth of Saccharomyces cerevisiae has been studied. Generally the experiments resulted in the following findings: Low zinc concentrations reduce the toxicity of cadmium while high zinc concentrations intensify the effects of cadmium. Zinc does not decrease the growth inhibition by mercury. The actions of cadmium and mercury are not changed by lead, but 5 X 10(-4) M lead prevent completely the increase of the growth intensity caused by zinc. Combinations of toxic concentrations of cadmium and mercury show a synergistic lengthening of the lag period, but their cumulative influence on the growth rate is lower than the sum of the corresponding inhibition effects.