A program of detoxification of heroin addicts by the use of oral methadone produced a series of patients who developed pulmonary granulomatous mass lesions as the result of the intravenous use of the oral form of the drug. Talc, used in the preparation of the tablet, seems to be the offending substance. Besides producing a diffuse interstitial granulomatous reaction, conglomerate masses in the upper lung zones were also noted. This radiographic pattern can occur rather rapidly from the background of fine diffuse interstitial micronodularity. The latter may be subtle, but can change to mass lesions associated with lung contraction, volume loss in the upper lung zones, and hyperinflation in the lower lungs. The mechanism of formation of mass lesions is unknown, but individual host reaction and immunologic mechanisms probably play a role. The development and progress of such a process is described in four heroin addicts.