Tobramycin is an aminoglycoside aminocyclitol antibiotic with pharmacological similarities to gentamycin. Twenty-one of 30 patients with a severe or complicated Gram-negative urinary tract infection were cured by treatment with a 5-day course of tobramycin. No side effects were noted. This drug should prove beneficial for the treatment of severe Gram-negative sepsis, and promises to be particularly valuable for infections due to Pseudomonas aeruginosa. Dosage schedules for administering tobramycin to patients with renal function impairment are presented, together with some observations on its intravenous injection by bolus. A single dose of tobramycin has proved effective for initiating the antibacterial treatment of patients with acute pyelonephritis. The important concept of the differing concentrations of an antibiotic in the urine from kidneys of unequal function is discussed.