2-Butoxy-5-aminopyridine and certain salts were found to have high in vitro activity in the inhibition of growth of the Mycobacterium tuberculosis. Some strains were inhibited in dilutions up to 1/1oo,ooo,ooo. This tuberculostatic action was specific for organisms belonging to the genus Mycobacterium and was not reversible by [rho]-aminobenzoic acid, methionine, riboflavin, adenine, pantothenate, thiamine, biotin, nico-tinic acid, uracil, guanine and other substances, some of which antagonize sulfonamide activity. The activity of 2-butoxy-5-aminopyridine is bacteriostatic rather than bactericidal. These substances act by interference with some essential metabolic process common to spp. of Mycobacterium but which is lacking, has readily available alternatives, or is nonessential in other genera of organisms.