Bactericide (I) such as formaldehyde or formaldehyde releasing compound is used in a composition to combat Mycobacterium (II), where overdosage of (I) does not promote the growth of (II) and effectiveness of (I) against (II) is greater than the effectiveness of 2,2',2''-(hexahydro-1, 3,5-triazin-1,3,5-triyl)triethanol (III) or (I) (in less concentration) in combination with (III) exhibits the same effectiveness. ACTIVITY : Antibacterial. MECHANISM OF ACTION : None given.