Railroad workers (377) were studied. The prevalence of asbestos-related disease was investigated. Conventional with more recently adopted criteria were compared for defining abnormal lung function. The test results of those who performed reproducibly on spirometry were compared with those who did not. Medical and occupational histories, flow-volume loops and posteroanterior and lateral chest radiographs were obtained. Single-breath CO diffusing capacity (DLCO) was measured and chest auscultation was performed. Related to time since onset of exposure, pleural plaques occurred in 22.9%. There was radiographic evidence of interstitial disease in 1.6%. Reduced single-breath DLCO (12.4%), crackles (18.4%) and dyspnea (49.6%) were significantly associated with asbestos exposure. The prevalence of restriction and obstruction was 5.1 and 12.4%, respectively, but differed (P = 0.0001) with the definition criteria selected. The proportion with each of these abnormalities was higher in the nonreproducible group. That group was older, with more pleural plaques and chronic bronchitis. Railroad workers are a group at risk for asbestos-related disease. Extent of disease and assumptions about causality are likely to vary with definitions of normalcy and the use of reproducibility criteria.