Antibiotics are the principal cause of drug-associated nephropathy. They are responsible for acute interstitial nephropathy (AIN) or acute tubulo-interstitial nephropathy (ATIN) due to two different pathophysiologic mechanisms: a drug-induced immunologic process and direct action due to drug accumulation. 1) Ain of immunologic origin. These are rare and are induced either by beta-lactamines or by rifampicin. Among the beta-lactamines, methicillin is the most often responsible, while penicillin and ampicillin are less often, and only rarely are carbenicillin, oxacillin, nafcillin, cephalothin and cephalexin. Macroscopic hematuria occurring 10 to 15 days after initiation of treatment usually reveals the renal involvement. It is associated with or preceded by fever, skin eruption and blood eosinophilia. Renal insufficiency (RI) is not severe and rarely requires hemodialysis (HD). The course is usually favorable. Rifampicin-induced AIN is observed in two circumstances, either during intermittent treatment or when previous treatment is resumed. Macroscopic hematuria is rare and RI often severe. Anti-rifampicin anti-bodies are usually found. 2) ATIN due to direct toxicity. Several classes of antibiotics may be responsible: cephalosporins, polymyxins or cyclins, but it is usually observed with aminoglycosides (AG). The incidence of renal involvement due to the latter group is estimated to be 4 to 10%. Nephrotoxicity is initially reflected by polyuria, tubular proteinuria and increased enzymuria, followed by cylindruria and reduced glomerular filtration. HD is rarely required. The proximal tubule is predominantly affected; pathological findings are disappearance of the brush border and tubular necrosis. Electronic microscopy shows lysosomal alterations with numerous myelinic bodies. Tubular regeneration occurs within 15 to 30 days.(ABSTRACT TRUNCATED AT 250 WORDS)