A controlled study of the value of bacterial vaccines in 118 infants and children subject to repeated episodes of asthma associated with respiratory infections is described. Both vaccine-treated and a control group, treated similarly except for omission of bacterial vaccines from hyposensitization therapy, were compared before and at the end of a 3½-year period. When the maximum dose of vaccine was administered every 28 days, no statistically significant differences were observed between the two groups with regard to the following criteria: 1) number of asthmatic episodes per year; 2) average number of days wheezing per year; 3) average number of days school missed per year during asthmatic episodes; 4) number of children with 100%, 50-100% or 0-50% reduction in number of asthma attacks per year. In the vaccine-treated group the type of vaccine used did not appear to influence the degree of improvement as reflected in number of asthmatic attacks per year in the last year of the study compared to the year preceding the study. The incidence of positive skin tests to stock bacterial vaccines and a commercially prepared vaccine was approximately the same in both groups.