A patient with pulmonary disease due to Mycobacterium terrae, a soil saprophyte seldom encountered as a pathogen, is described. The strain was isolated repeatedly from the sputum and gastric washings of the patient in whom no evidence of impairment of cellular or humoral immunity was found. Bacteriological conversion followed initial therapy with isoniazid, rifampicin, pyrazinamide, ethambutol, streptomycin and pefloxacin for two months, followed by maintenance therapy of isoniazid, rifampicin and pefloxacin.