We surveyed 270 asbestos factory workers and 222 control subjects matched for age to assess the usefulness of listening for fine discontinuous adventitious lung sound (fine crackles) in detection of the early stages of interstitial fibrosis of asbestosis. Fine crackles at both bases were heard more frequently in asbestos workers (32.2%) than in controls (4.5%) (P less than 0.01). The presence of bilateral basal crackles was related to the duration of asbestos exposure and occurred before abnormalities could be detected by chest radiography. Two observers examined 74 workers randomly chosen from among 270 asbestos workers and found inter-observer agreement to be high (91.9%). There was close agreement between findings on chest auscultation and sound recordings.