During a 2.5-year period, 52 patients at Yale-New Haven Hospital had Mycobacterium gordonae recovered from specimens obtained by suction at bronchoscopy; 2 of them also had smears positive for acid-fast bacilli. Almost all of the isolates came from patients bronchoscoped by the same physician, one of 4 who performed the procedure during that period. Only this physician added one drop of green dye, stored in a 100-ml bottle, to the cocaine used for topical anesthesia during the procedure; cultures of the dye yielded Mycobacterium gordonae. Contamination with this organism, a cause of positive acid-fast smears, may result in an initial inappropriate diagnosis of Mycobacterium tuberculosis.