Minocycline, rifampin, sulfadiazine, and a combination of minocycline and rifampin were studied for efficacy in eradication of meningococcal infection in families of patients with meningococcal disease in São Paulo, Brazil. The rate of meningococcal infection two weeks after treatment of carriers with sulfadiazine (49%) was greater than the rates after treatment with minocycline (17%), rifampin (9%), or the combination of minocycline and rifampin (0%). While persistence of carriage was not statistically different in the groups receiving minocycline or rifampin, seven of 69 persons (10%) receiving rifampin alone were subsequently found to carry rifampin-resistant meningococci. No minocyclineresistant meningococci were found. The most effective regimen tested for eradicating meningococcal carriage was the combination of minocycline and rifampin, but unpleasant side effects were experienced by 33% of the persons who received this combination.