During March-april 1996, a physician in the Denver area administered intramuscular injections of a preparation labeled "adrenal cortex injection" to 69 patients in Colorado as part of a weight-loss regimen. As of August 7, a total of 47 (68%) of these persons were reported to have developed abscesses (diameters ranging from 0.5 cm to 4.0 cm) at the site of injection (either gluteal or deltoid muscle). An investigation of these episodes by the physician and the Colorado Department of Public Health and Environment identified Mycobacterium abscessus as the cause of the infections. This report summarizes preliminary findings of the ongoing investigation, which indicate that injection-site abscesses were associated with contaminated injectable preparations.