The data on the toxicity of netilmicin in laboratory animals as well as preliminary data in man are reviewed. Netilmicin is less toxic to the VIIIth nerve than is gentamicin in all species tested. The data suggest that it probably is less ototoxic than tobramycin, although confirmatory studies should be performed. Netilmicin is also nephrotoxic than gentamicin in all species tested. It is less nephrotoxic than tobramycin in the rat and dog. Comparisons in the rat suggest that netilmicin has a flat dose--response curve that resembles the curve produced by streptomycin. In animals, netilmicin produces more neuromuscular blockade than gentamicin; however, neuromuscular blockade with aminoglycosides in man is rare and thus far no episodes have been associated with netilmicin during clinical investigation. Initial clinical studies in man indicate that netilmicin is efficacious and well tolerated. Presently available data suggest that netilmicin offers distinct advantages over older aminoglycosides. Final conclusions must await prospective randomized double-blind trials in man.