Tobramycin sulphate, a bactericidal aminoglycoside antibiotic, has been evaluated worldwide in 3,506 patients. Drug-related adverse effects were reported by the investigators in 3.9% of the cases, and included reactions in the nervous system (ototoxicity) in 0.6% and in the kidney in 1.5%. Effects of doubtful relationship to tobramycin occurred in 6.6% of the cases. The effects were usually reversible, although infrequently altered renal or eighth-nerve function appeared to persist in some of the patients. There were no deaths or instances of renal shutdown as a result of tobramycin therapy. Therefore, under the clinical conditions in which it was evaluated, tobramycin appeared to be well tolerated. The association of toxicity with various "risk factors" is discussed.