The use of the agar plate method as a screening test for detecting the toxicity of chromium and copper and of effluents from the tannery industry was evaluated. The bacteria Bacillus cereus and Escherichia coli were used as test organisms. The toxicity of chromium and copper on B. cereus was demonstrated at concentrations as low as 2 and 0.5 μg/spot, respectively. A linear relationship between the chromium concentration (μg/spot) and the diameter (mm) of the clear inhibition zone on the agar plates was observed between 2 and 20 μg for B. cereus and between 10 and 50 μg for E. coli. For copper the linear relationship was between 0.5 and 50 μg/spot for B. cereus and 5 and 50 μg/spot for E. coli. Bacillus cereus was more sensitive than E. coli to these tests. Results with tannery wastes showed that the method is applicable to detect environmental contaminants and the procedure is a convenient and economical tool for screening toxicity of chemical compounds and industrial wastewaters. © 1996 by John Wiley & Sons, Inc.