The mechanisms by which Streptococcus pneumoniae spreads from person to person are poorly understood. In this study, optimal methods for sampling, isolation, and identification of S. pneumoniae from healthy carriers were investigated. Factors influencing carriage rates were analyzed. Findings included the importance of pharyngeal rather than of nasal sampling in adults, the greater sensitivity of mouse inoculation compared with direct streaking of blood agar plates, and the superiority of the Quellung reaction with omniserum over the optochin disk as a means of identification of S. pneumoniae. Carriage rates were highest in children of preschool (35%) or grammar school (29%) age and in adults with preschool children in the family (18%). Rates were lowest in adults without preschool children in the family (2%-9%).