Five Egyptian male farmers, aged 12 to 23 years, with urinary schistosomiasis and proven Salmonella bacteriuria and bacteremia developed massive proteinuria. Treatment of the Salmonella infection with ampicillin resulted in rapid cessation of proteinuria with return of normal renal function, and improvement in maximal urine concentrating ability. All five patients had markedly depressed levels (<50 mg/100 ml) of complement C3 in serum on admission. Levels returned to normal 1 month after treatment with ampicillin. It is suggested that under certain circumstances prolonged Salmonella infection of the kidney (possibly through an immunologic mechanism) may lead to the nephrotic syndrome.