The efficacy of cefaclor and rifampin in eradicating Haemophilus influenzae type b (HITB) from the nasopharynx of day care center and household contacts of children with HITB meningitis was evaluated. In 38/50 children treated with cefaclor, the carrier state persisted, a failure rate of 76%. Although cefaclor failed to eradicate HITB from many carriers, an appreciable reduction in the intensity of colonization following treatment was noticed. When rifampin was used in 17 children who had failed to respond to cefaclor, persistence of the carrier state with HITB was found in only two children, a failure rate of only 12%. During the study, two episodes of invasive HITB disease were documented to be acquired from sources other than the index cases or from children who were screened, which suggested the need to reevaluate the usually recommended strategy to screen for carriage and to treat only the immediate contacts 6 years of age and younger. Furthermore, the most appropriate agent for eradicating nasopharyngeal carriage of HITB awaits additional studies.