The oxidation of benzoate by Mycobacterium lacticola previously grown in the presence of the substrate is relatively insensitive to streptomycin. The % inhibitions were 25, 30, and 33% for 50, 100, and 200 7/ml. of streptomycin HC1, respectively, as detd. by the Warburg technique. The oxidation of benzoate by the normal strain was inhibited 44, 82, and 100% by the same amts. of streptomycin. Similar results were obtained with p-hydroxyben-zoic acid. There is always a latent period before the normal strain oxidizes these substances which does not occur with organisms previously grown in their presence. It is concluded that the inhibition observed is due to supression by streptomycin of formation of adaptive enzymes by M. lacticola.