A double-blind, randomized, controlled trial of a 14-valent Streptococcus pneumoniae polysaccharide vaccine, with saline as placebo, was performed on 1,273 healthy children six to 54 months of age. Different dosage regimens were used for children younger and older than two years of age. The vaccine was well tolerated. Follow-up continued for two years, during which time 95% of mothers submitted diaries of their children's respiratory-tract and otic symptoms. Data from diaries and medical and hospital case notes failed to reveal consistent or significant benefits in those who received the vaccine. In the first 16 months after immunization, recipients of placebo experienced an average of 0.69 episodes of otitis media per child, compared with 0.63 in recipients of vaccine (P = .6). Recipients of vaccine had no consistent reduction in days of respiratory morbidity, antibiotic consumption, hospitalization, or visits to a physician, when compared with recipients of placebo.