An analysis of skin prick reactions in 500 consecutive patients referred for investigation and management of asthma showed that 240 patients had multiple positive reactions. Of these patients 46% had positive reactions to Aspergillus and they differed from patients with multiple positive reactions excluding Aspergillus by having onset of asthma at a younger age and being more atopic. Precipitins to Aspergillus were present in the serum of twenty-six of seventy-one consecutive patients in whom these were looked for. Thirteen of the patients with positive precipitins had chest radiograph shadows compatible with allergic bronchopulmonary aspergillosis (ABPA) and in eight of these there was sufficient evidence to make a diagnosis of ABPA. These results were obtained in a region where ABPA had never been previously recognized and they highlight the importance of routine skin prick testing with Aspergillus antigen and of awareness of ABPA in making this diagnosis.