An aeromycological study has revealed the preponderance of Aspergillus fumigatus at the bagasse-containing sites in sugar-cane mills located in the northwestern part of the Punjab State. The fungus was frequently isolated from the sputum cultures of the mill workers and a significant number of the workers were positive reactors when challenged intracutaneously with aspergillin. Immediate Type I and late Arthus Type skin hypersensitivity was observed in 10.6% and 4.4%, respectively, of the 548 workers investigated. Incidence of hypersensitivity was particularly high among workers having chronic respiratory problems. During a sample survey of 238 workers having chronic respiratory diseases, diagnoses of allergic bronchopulmonary aspergillosis, and allergic bronchopulmonary candidiasis based on positive clinical and laboratory findings, were made in 17 (7.1%) and in only 4 (1.7%) of the cases, respectively. Evidence is presented to support that the epidemiology of allergic bronchopulmonary aspergillosis, but not of allergic bronchopulmonary candidiasis, may have an occupational dimension.