PNEUMONIA caused by the "opportunistic" organismPneumocystis cariniioccurs mainly in premature infants and immunocompromised children.1-2We reportP cariniicausing pneumonia in a previously healthy American-born 7-month-old infant who showed no evidence of immune deficiency. Report of a Case A 7-month-old boy was admitted to Kings County Hospital, Brooklyn, NY, in July 1975 with clinical and roentgenographic evidence of right middle lobe pneumonia. Three weeks before admission, right middle lobe pneumonia had been diagnosed, and the child was given penicillin V by mouth, 250,000 units four times a day for seven days, followed by 125 mg of erythromycin estolate suspension, three times a day for seven more days. The child continued to have cough and mild respiratory distress. At the time of admission, the child had a temperature of 38 °C and moderate respiratory distress. Auscultation demonstrated decreased breath sounds and rales over the right side of the