The induction of chromosome aberrations, micronuclei, and sister-chromatid exchanges (SCEs) was examined in cultured lymphocytes of 27 vineyard growers exposed to pesticides. Cytogenetic examinations were performed during the prespraying period, a month after spraying, and at the end of the spraying season. For comparison purposes, the same cytogenetic monitoring program was applied to two control groups. The first consisted of 15 individuals from a nearby town, and the second consisted of 20 volunteers living 200 km from the vine-growing area (reference control group). A positive, though low statistically significant (P < 0.017) difference in the yield of unstable chromosomal aberrations in exposed sprayers was observed compared with both control groups during the prespraying period. The mean group value of micronuclei in exposed workers averaged 5.41 per 1000 binucleated cells, with individual means ranging from 0 to 15. In both control groups, the yield of micronuclei averaged 5.09 per 1000 binucleated cells, with individual means ranging from 1 to 10. No statistically significant (P < 0.5) differences in yield of micronuclei were found in exposed subjects compared with both control groups. Significant individual variation (F = 14.09, P < 0.000) in SCE frequency was observed in exposed subjects, as well as in both control groups (F = 14.09, P < 0.000). A month after spraying, the average incidence of unstable aberrations in pesticide sprayers was 0.22%, and the yield of micronuclei averaged 17.78 per 1000 binucleated cells, with individual means ranging from 7 to 28. The incidence of micronuclei a month after spraying in exposed subjects was elevated (statistically significant at P < 0.01) in comparison with the prespraying period, while the difference in the yield of chromosomal aberrations in exposed subjects was insignificant (P < 0.5). At the end of the spraying season, the average incidence of unstable aberrations in exposed subjects was 0.79%, and the yield of micronuclei averaged 39.92 micronuclei per 1000 binucleated cells, with individual means ranging from 21 to 62. The appearance of more than one micronucleus per binucleated cell was related to the results on chromosome aberrations. The frequencies of chromosomal aberrations and micronuclei were significantly higher (P < 0.001, P < 0.000) in the exposed group than in their matched control groups. The yield of micronuclei in pesticide sprayers at the end of the season was higher than expected with respect to chromosomal aberration frequency, which provides some evidence that some of the micronuclei are induced by the spindle-inhibiting effects of pesticides. A statistically significant (P < 0.003) difference in micronuclei in the first control group was observed compared with the reference control group at the end of the spraying season. With respect to the incidence of micronuclei in the control group in the vine-growing area, a poor but positive correlation (r = 0.074, P < 0.104) with duration of the spraying season was found, which is probably due to airborne pesticides in the vine-growing area. SCE frequencies of the workers' lymphocytes were not significantly changed due to the exposure. The yield of aberrations as well as that of micronuclei in exposed subjects correlated positively (r = 16, P = 0.016) with duration of exposure.