Enzyme inhibition of sewage microorganisms by heavy metals was studied. The degree of inhibition varied with metal and organism. The Michaelis-Mentan model was used to show that zinc, trivalent chromium, and copper were more toxic to sewage bacteria, whereas silver and nickel were more toxic to sewage fungus Geotrichum candidum. A competitive inhibition was detected for sewage bacteria, but the same metals showed a mixed non-competitive inhibition for Geotrichum candidum. The results imply that silver and nickel could make Geotrichum candidum more competitive in sewage than bacteria. Other conditions under which Geotrichum candidum can grow better than sewage bacteria include low temperature, high chloride content and the presence of asphalt photosensitization. (Author)