Mycobacterium chelonae, a rapidly growing species, is a significant cause of fever in neutropenic patients. We describe three febrile neutropenic patients at the Royal Free Hospital from whom this organism was isolated on several occasions. The condition of the first patient improved as the neutrophil count recovered. The second patient developed pulmonary disease and required surgical resection of a pulmonary lesion. The third patient, who had rapidly progressive, diffuse pulmonary disease, responded to an antibiotic regimen including erythromycin and ciprofloxacin. Both our findings and reports in the literature suggest that neutropenia may be a major risk factor for disseminated infection due to M. chelonae and that treatment is effective only after the recovery of the neutrophil count.