The author and his coworkers reported that, under their test conditions, the emergence of streptomycin-resistance and isoniazid-resistance in the sensitive strain of Mycobacterium avium was prevented by the addition of relatively low concentrations of sulfathiazole, and the preventing effect of sulfathiazole was completely antagonized by the addition of paraaminobenzoic acid or folic acid⁽¹⁾⁽²⁾. In the present paper, the combined effect of sulfathiazole and streptomycin or isoniazid on the emergence of streptomycin-resistance or isoniazid-resistance in the sulfathiazole-resistant strain was observed.