The use of aminoglycosides and cephalosporins is fairly often complicated by acute renal failure (ARF), particularly so if overdoses are used and baseline renal function is impaired. The course of ARF and outcome of treatment have been analyzed in 51 patients. ARF was caused by a nephrotoxic effect of aminoglycosides, cephalosporins or a combination thereof (ARF, type A) in 30 (58.8%) patients, and a combination with other factors (hypotension, arterial hypertension, sepsis) in 21 (41.2%) patients (ARF, type B). Nephrotoxic effect was more commonly produced by a ceporin-gentamicin combination (in 34 (66%) of 51 cases). Nineteen (55.8%) of the 34 patients died, in spite of extracorporeal detoxication treatment (peritoneal dialysis, hemodialysis), which way be attributed to a severe original condition (mostly, due to severe sepsis, original functional renal insufficiency, etc.) rather than the nephrotoxic effect of antibiotics. Hyperazotemia without marked oliguria is a specific feature of ARF, induced by nephrotoxic action of antibiotics. Preventive principles are proposed.