A case with the characteristics of allergic bronchopulmonary aspergillosis is described. The species of Aspergillus involved, A. ochraceus, has not previously been found in this disorder. The organism had antigenic properties distinct from five other species of Aspergillus most commonly associated with allergic bronchopulmonary aspergillosis. The patient had immediate skin test, immunodiffusion, and radioallergosorbent reactivity to the species. Four per cent of 112 serum samples from others suspected of having allergic bronchopulmonary aspergillosis had precipitins to A. ochraceus only. It may be necessary in some cases to prepare and test extracts of the patient's Aspergillus isolate in order to confirm the diagnosis.