A survey of the safety and effectiveness of tobramycin, a newly developed aminoglycoside antibiotic, was assessed in 116 septic surgical patients. For comparison, the final 52 cases were randomized with 51 similarly infected patients who were treated with gentamicin. The two antibiotics gave equally good results when evaluated bacteriologically and clinically. Nevertheless, gram-negative infections appeared more likely to be susceptible to tobramycin than to gentamicin. No toxicity to the liver or bone marrow was observed. Although there were 13 cases of nephrotoxicity and 4 of ototoxicity, only one instance of such an adverse drug reaction could be attributed to parenterally administered aminoglycoside alone. In fact, topical neomycin and established renal damage caused by prior episodes of shock or dehydration appeared to be significantly more responsible for such adverse effects.