Six patients with acute gram-negative bronchopulmonary infection were treated with amikacin (15 mg/kg per day) administered intramuscularly in two equal doses at 12-hr intervals for 10-13 days. Two patients had underlying nonspecific pulmonary disease, two had advanced bronchocarcinoma, and two had extensive bronchiectasis (due to chronic aspergillosis in one patient). The pathogens were Pseudomonas aeruginosa in three patients, and Haemophilus influenzae, Klebsiella ozaenae, and Enterobacter cloacae each in one patient. Five patients recovered completely, with resolution of fever and other acute symptoms and elimination of the causative organism from sputum cultures. A moribund patient with advanced metastatic bronchocarcinoma died two days after the treatment with amikacin had been completed; the last specimen of sputum was still positive for P. aeruginosa. Tests of liver and renal function and blood counts revealed no abnormaltities. Complete audiometric survey showed no hearing loss. Nystagmography revealed reversible, lessened caloric response in some patients. Amikacin was well absorbed from the site of intramuscular injection. Levels of amikacin in serum varied among the subjects and, in some cases, for individual patients on different days.