Pneumocystis carinii pneumonitis: a serological study.

Sera from 23 proven or clinically suspected cases of Pneumocystis carinii pneumonitis (PCP) in immunosuppressed patients predominantly with acute lymphoblastic leukaemia, and from 91 normal people, were examined for antibody to P. carinii by indirect immunofluorescence. Low levels of antibody were found in 51 of 91 normal people and elevated or rising titres of antibody in 18 out of 21 cases from whom paired or serial convalescent sera could be obtained.