The bacteriophage pattern of 24 classified acid-fast microorganisms is presented and compared to that of a group of unclassified mycobacteria isolated from tuberculous patients. Of 33 unclassified acid-fast cultures studied 24 (73%) were typed satisfactorily; these comprised 93% of the cultures isolated from gastric lavage, 75% of those isolated from urine, and 29% from sputum. The majority of these fell into aMycobacterium smegmatisphage pattern.