Peripheral lymphocytes of 3 groups of adult subject (28 workers occupationally exposed for 4 years to epichlorohydrin [ECHH], 34 matching controls and 21 subjects of the general population (control group) were cytogenetically analysed. In total, 11 806 metaphases were scored. The following frequencies of aberrant cells (bearing mostly chromatid and chromosome breaks) were detected in individual groups: ECHH-exposed group 3.12%; matching controls 2.06%; general population control group 1.33%. The results seem to indicate that even the concentration of 1 mg ECHH/m3 was capable of increasing the frequency of aberrant cells in the occupationally exposed group of workers.