The background and the recent clinical trials of the current pneumococcal vaccine, especially as they pertain to the institutionalized elderly, are described. Previous studies with a vaccine containing types 1, 2, and 3 demonstrated a reduced incidence of putative pneumococcal pneumonia among vaccinated elderly persons as compared with a control population of unvaccinated subjects. Capsular polysaccharides from types 1, 3, 4, 6, 7, 8, 9, 12, 14, 18, 19, and 23 (Danish nomenclature) were selected for inclusion in the current vaccine because these types accounted for ∼75% of the isolates of Streptococcus pneumoniae from patients with positive blood cultures in acute-care general hospitals. Purified polysaccharides from these types plus types 2, 5, and 25 were combined into hexavalent, dodecavalent, and tridecavalent vaccines. Mild, local reactions were noted among 40%–60% of elderly persons who received the vaccine; fever was noted in 54ctJo of definite cases of pneumococcal pneumonia and 65% of putative cases were caused by vaccine types of organisms. Certain nonvaccine types, including 17, 11, 15, and 34, were found more frequently in this study than in the study of patients with bacteremic infections in acute-care settings. Several questions related to the effect of pneumococcal vaccine in these semiclosed populations remain unanswered, e.g., (1) what percentage of pneumococcal disease is caused by serotypes represented in the current vaccine, and (2) what will be the net effect of the current pneumococcal vaccine if it becomes more widely used?