One aspect of Drs. Cox and Hughes' timely report on nocardiosis1 merits additional inquiry and comment. What was the time relationship between the appearance of nocardial disease and treatment of the Pneumocystis carinii pneumonitis in patients 2 and 4? Were these patients on antipneumocystis therapy at the time of recognition of nocardial infection and, if so, for how long and with what agents? If they were being treated with a combination of a sulfonamide and a folic acid antagonist (e.g., pyrimethamine or trimethoprim), do these cases represent the development of nocardiosis while on "specific therapy" (i.e., sulfonamides)?