Toxicity of heavy metals and insecticides on the slime mold Physarum polycephalum was investigated in order to examine and estimate with ease the toxicity of environmental and occupational contaminants and also to study the effects of various agents on the cell membrane. Changes in survival time and in membrane potential of the slime mold were measured using a double chamber method. The results obtained suggest that their toxicity for the slime mold is accompanied by some change in the cell membrane, and that studies on toxicity for various chemical substances in the slime mold can be used as a screening method.