DNA damage was measured by using the alkaline comet assay and the chromosomal aberration (CA) test using peripheral blood samples from 45 pesticide sprayers from Cayambe, Ecuador. From a total of approximately 200 nuclei scored for each donor with the comet assay, a highly significant increase in DNA migration was observed when compared with a similar unexposed control population. Additionally, in the CA test, the exposed individuals were found to be significantly different when compared to the control population. Polymorphisms for the CYP 1A1 (Msp I and Ile/Val) in exposed individuals were analyzed by PCR-RFLP and allele-specific PCR techniques. No association was found between the polymorphisms and higher levels of DNA damage as assessed by the comet assay.