Chromosome aberrations and sister chromatid exchanges (SCEs) in lymphocytes of peropheral blood as an indicator which could evaluate the effects of mutagenicity after in human exposure to mixed-organic solvents were measured. This study was conducted using 33 shoe making workers occupationally exposed to organic solvents and 33 unexposed control. The results were as follows. 1. The mean air concentrations of n-hexane, toluene, ethyl acetate in working environment were 9.8-14.8, 31.7-45.4 and 4.4-7.6 ppm, respectively. 2. The frequencies of chromosome aberration in exposed workers to mixed-organic solvents and the unexposed were 1.12+/-1.24, 0.36+/-0.70, respectively and their differences were statistically significant (p<0.01). However, the SCE frequencies were not statistically significant between the both groups. 3. The frequencies of chromosome aberration and SCE were no statistically differences by sex, smoking and drinking.