Examination of the inhibition of the growth of E. coli by air pollution mixtures has indicated that the activity of aldolase and of glutamic dehydrogenase is inhibited. The oxidation of sulfhydryl groups was one of the sites of reactivity of the pollutant mixture. Attempts to fractionate or concentrate the biologically effective material has served to indicate that biological effectiveness did not reside in a single component and implicated polar material(s). Since the effect of the pollutant mixture on succinoxidase system was comparable to that of 2-nitropropane, the latter may serve as a model compound for the examination of effects on particular enzyme systems.