In order to determine the incidence of bronchopulmonary aspergillosis in patients with other types of pulmonary pathology, 586 in-patients, out-patients and controls were examined during the period 1968–1970 in Baguley Hospital, Manchester, England. It was found that from the 344 in-patients and out-patients with other pulmonary pathology, 6 had a definite diagnosis of allergic aspergillosis. 1 had pulmonary aspergilloma while 53 other patients demonstrated some evidence of bronchopulmonary aspergillosis. These 53 patients had insufficient criteria to be classified in one of the recognised forms of aspergillosis. The number of controls examined was 242, none of whom were found to have allergic or other forms of aspergillosis. Eleven of these had a positive immediate skin test the other tests being negative. In addition to the above groups 534 patients with bronchial asthma, attending the out-patient department, were investigated with multiple intradermal tests, including Aspergillus fumigatus. Positive intradermal. Aspergillus test was found in 130 of the patients with bronchial asthma. This investigation showed that the bronchopulmonary aspergillosis is more prevalent in patients with a pulmonary disease than in persons without this pathology.