Amikacin is a new aminoglycoside antibiotic related chemically to kanamycin. It has broad spectrum activity against most gram-negative bacilli. The most important advantage of this aminoglycoside is its activity against gram-negative bacilli which are resistant to gentamicin. Amikacin was given to 22 cancer patients with 24 serious infections produced by gram-negative bacilli resistant to gentamicin and 13 (54 per cent) were cured. Response to amikacin was related to the patients's neutrophil count at the time of infection; neutropenic patients having a lower response rate (30 per cent vs 71 per cent). Side effects included nephrotoxicity (12 per cent) and audiotoxicity (5 per cent). Amikacin is an effective new antibiotic for patients with severe infections produced by gram-negative bacilli resistant to gentamicin.