The potential clastogenic effects of pesticides was investigated in 71 floriculturists exposed to complex chemical mixtures. Exposed and referent subjects were selected from the same geographical area located in north western Italy. A significant association between micronuclei frequency and occupational exposure to pesticides was found (RR = 1.25). A positive dose-response gradient was observed with years of employment (used as an index of cumulative exposure) as a floriculturist. Individuals working exclusively in greenhouses (confined spaces) showed higher micronuclei levels than subjects working in open fields. The study supports the hypothesis that human exposure to pesticides causes a clastogenic damage.