To determine whether occupational exposure to a complex mixture of pesticides results in a significant increase in the level of cytogenetic damage, a follow-up study was planned on 39 greenhouse workers from Almería (southeastern Spain). Taking into account that pesticide exposure can be season-related, two blood samples were taken from each individual at different times: one in a period of high exposure (sample A, spring-summer) and the other in a period of lower exposure (sample B, autumn-winter). Using the cytokinesis block micronucleus technique the frequency of binucleated cells with micronuclei (BNMN) and the cytokinesis blocked proliferation index (CBPI) were determined in peripheral blood lymphocytes. The results obtained indicate that there were no statistically significant differences in BNMN frequencies between the two sampling periods nor between exposed and controls. ANCOVA analysis of repeated measures revealed that the age of the individuals showed a direct relation with BNMN in the first study period. With regard to CBPI, a significant and season-related effect was found.