Minocycline was 60 per cent effective in the elimination of group C meningococci from healthy carriers among naval recruits without selection of resistant strains Rifampin was 89 per cent effective against the same group of meningococci with the selection of rifampin-resistant strains. Rifampin-resistant strains did not spread to new susceptibles and only a few persisted in follow-ups of carriers. Selective treatment of group C carriers with minocycline and rifampin temporarily reduced the carrier rate in the treated men. Although a high percentage of group C carriers were cured by treatment with minocycline or rifampin, group C meningococci ultimately infected the same proportion of men as before treatment. Group C reacquisitions and spread of group C organisms to non-carriers rapidly overcame the curative effect of minocycline. Rifampin, however, was somewhat more successful in allowing non-group C to predominate in this population.