The potential clastogenic effect of pesticides was investigated in 56 (29 indoor and 27 outdoor) agricultural workers exposed to complex chemical mixtures. Exposed and referent subjects were selected from the same geographical area located in Ionia, province of Thessaloniki, Greece. Chromosome aberrations (CA) and sister chromatid exchanges (SCE), were studied in peripheral lymphocytes. Comparison between workers and control group revealed that the individuals exposed to pesticides showed substantial clastogenic effects (CA = 2.66% compared to 0.53%, P < 0.001), in their lymphocytes without indication of increases in their basal frequency of SCE. Moreover, the condition of exposure has been found to influence the CA frequency. It was observed that individuals working exclusively in greenhouses (confined spaces) showed higher CA levels than subjects working in open fields (3.37 versus 1.88, P < 0.01). No significant difference in their expression of CA between smokers and non-smokers was found. The present chromosome study included workers living in the close vicinity of a large industrial zone near Thessaloniki. The percentage of CA in these indoor sprayers was higher compared to our previous study carried out in a different area of Thessaloniki, free of industrial plants (3.37% compared to 2.14%, P < 0.02).