Workers chronically exposed to whole-body vibration and noise are known to develop pathophysiological and psychological disturbances. The frequencies of sister chromatid exchanges (SCEs) and of cells with high frequencies of SCEs (HFCs) were analyzed in lymphocytes of 50 workers occupationally exposed to vibration and noise and of 34 controls. The exposed group included: individuals operating hand-vibrating tools (group 1), 'test-cell operators' (group 2) and 'run-up' operators (group 3) from an air base and helicopter pilots (group 4). The statistical analysis of the mean SCE count per cell was carried out by multiple regression analysis, comparing various predictor variables: exposure group, duration of exposure, age and cigarette consumption. Only cigarette consumption and exposure group were found to be significantly correlated with the mean SCE frequency. After allowing for the effects of smoking, the analysis indicates that: (1) there was no significant difference between group 1 and controls (p > 0.05); (2) the differences between group 2 and group 0, group 3 and group 0 and group 4 and group 0 were all highly significant (p < 0.001); (3) there was no significant difference between groups 2 and 3 (p > 0.05), nor between groups 2 and 3 combined and group 4 (p > 0.05); (4) exposure groups 2, 3 and 4 combined, had a significantly elevated mean SCE frequency compared to the control group (p < 0.0001). Statistical analysis of the proportion of HFCs was consistent with these results. Our data suggest that chronic exposure to whole-body vibration and noise may lead to an increase in the level of SCEs in man. The observed effects may not reflect a direct action of these physical agents on DNA. Alternative explanations may include some of the whole-body vibration and noise-induced or stress-induced pathophysiological alterations which may indirectly induce SCE formation.