The initiation of germination ofBacillus subtilisspores in complete medium and in phosphate buffer plus the enzyme subtilopeptidase is inhibited by chlorocresol, but the activity of the enzyme alone is not. This suggests that proteolytic activity is not the primary site of inhibition. Germination of spores of this organism can be initiated with one of each of five amino acids, viz.L-alanine,L-cysteine,L-valine,L-leucine, andL-isoleucine. The germination initiated by these amino acids is reversibly inhibited by chlorocresol. These results strongly suggest that the inhibitor prevents the initiation of germination of bacterial spores at the level of amino acid use, both in complete medium and with subtilopeptidase.