Clinical observations and immunological evidence are presented to support a diagnosis of late onset asthma due to exposure to Aspergillus niger in a 70-year-old man. Asthma occurred on only three occasions, each time approximately 6 hr after exposure to an area containing Aspergillus niger. His sputum culture contained the same organism. Immunological correlates using the Aspergillus niger extract included positive immediate and late skin tests, histamine release from leukocytes, and serum precipitins.