Pneumocystis carinii pneumonia or interstitial plasma-cell pneumonia is a common infection in Europe, where it occurs endemically or in small institutional epidemics. It affects chiefly premature or otherwise debilitated infants with a peak incidence at the age from 6 weeks to 4 months, but the disease has also been encountered in three adults.1 In this country three instances have thus far been recorded.2,3 and five other cases have been seen in Canada.4,5 Two further patients have recently been reported from Australia.6 These cases all occurred in infants and were recognized only at autopsy. Two other reports describe three patients with interstitial plasma-cell pneumonia, one seen in this country7 and the other two in Canada.8 In the former no mention is made of Pneumocystis organisms, while in the latter the agent could not be found. The European literature indicates that the clinical syndrome of this