A great deal of the flower cultivation in Italy is carried out in the western part of the Region of Liguria. The extensive use of pesticides professionally exposes floriculturists operating in this area to a complex mixture of compounds. The frequency of micronuclei in peripheral lymphocytes has been evaluated in 71 floriculturists and in a control group of 75 healthy blood donors living in the area. No correlation between age and micronucleus frequency was found in peripheral lymphocytes of the controls while an increase in this parameter was observed in the elderly of the exposed group. Our data suggest a sex-related effect in the induction of micronuclei. The frequencies of micronucleated lymphocytes were significantly higher in females than in males in both exposed and control groups (RR = 1.45, 95% C.I. 1.25-1.67). The main result of this study, however, is the observation of a significant increase in micronucleated lymphocyte frequency in people occupationally exposed to pesticides. The micronucleus frequency was 8.57/1000 for exposed persons and 6.67/1000 for controls (p < 0.05). A dose-response relationship with duration of exposure was apparent with a maximum increment of 71% in the frequency of micronuclei in subjects exposed for over 30 years.