Abstract
Serum samples from 145 children with no known immunosuppressive illness were examined by indirect immunofluorescence for antibody to Pneumocystis carinii. Positive antibody titres (greater than or equal to 1:8 dilution) were found in 69 children (48%). Antibody could not be detected in the remaining children. Previous studies have shown that at least 75% of children have antibodies to P. carinii by the age of 4 years. This study shows a lower percentage of children with detectable antibody. This may be related to geographical variation of antigen or possibly to the widespread use of co-trimoxazole.