Prospective randomized Norwegian multicenter clinical trial (11 hospitals) comparing tobramycin given once a day (new regimen) vs. three times a day (current regimen), with penicillin G, to cancer patients with febrile neutropenia. Tobramycin half life and postantibiotic effect is at best 12 hours. It has been questioned if tobramycin once a day is safe in patients with low levels of granulocytes when it is given with a drug like penicillin G which is not covering Gram-negative rods. Treatment of febrile neutropenia with penicillin G and an aminoglycoside is standard of care in Norway, and it is probably a regimen that is promoting antimicrobial resistance less than a broad spectrum beta-lactam.