A normal host can be colonized by mycobacteria other than tuberculosis (MOTT), resulting in bronchoscopic isolates of no clinical significance. In the acquired immunodeficiency syndrome (AIDS), Mycobacterium avium-intracellulare, Mycobacterium kansasii, and Mycobacterium xenopi have caused widely disseminated infection. To determine the usefulness of fiberoptic bronchoscopy (FB) in evaluating MOTT infection in AIDS, we reviewed MOTT cultures from 36 FBs, correlated these to clinical course, and identified MOTT isolates from cultures of all other sources in these patients. Of ten bronchoscopic MOTT isolates, seven were not related to lung disease or to dissemination within one month of FB. Of the four Mycobacterium fortuitum and seven M avium-intracellulare that did disseminate within one month, only two were reflected in bronchoscopic cultures. In patients with AIDS, bronchopulmonary MOTT colonization does occur. We recommend that standard criteria for pulmonary mycobacterial disease be applied. Negative bronchopulmonary cultures do not seem to exclude dissemination.