Pesticides are widely used in agriculture to enhance crop yields and to control disease vectors. Floriculturists work frequently in greenhouses and may be exposed to high levels of pesticides, which may result in adverse health effects. To evaluate the relationship between exposure to pesticides and DNA adduct formation in peripheral WBCs of Italian floriculturists, the nuclease P1 modification of a (32)P-postlabeling assay was used to analyze WBC DNA from floriculturists (n = 26) and matched controls (n = 22). DNA adduct-positive samples were more frequent in floriculturists (11/26; 42%) than in matched controls (2/22; 9%) (P < 0.01). Slightly higher frequencies of DNA adduct-positive samples were observed in floriculturists > or = 44 years of age (53%) and in female floriculturists (57%). Floricultural practice was found to be associated with a significantly higher DNA adduct-positive rate in WBCs (rate ratio, 5.12; 95% confidence interval, 1.1-23.7) after allowing for the effects of age and gender. These two latter covariates were not significantly associated with DNA adduct-positive rates. The quantitative levels of DNA adducts were significantly higher in floriculturists than in matched controls according to the Mann-Whitney nonparametric statistic (P = 0.0052). The median adduct level for positive samples among floriculturists was 1.5/10(8) bases. A specific, well-visible spot, named alpha adduct, was detected in 7 out of the 11 DNA adduct-positive samples from floriculturists but in none of the (22 + 20) referent samples (P = 0.0004). The presence of pesticide-related DNA adducts was confirmed clearly using the butanol extraction procedure. Six of 8 floriculturists and 0 of 10 referents were found positive with this method. The median adduct level for positive samples was 6.0/10(8) bases. Two strong spots close to the origin could be identified in all six positive floriculturists, using the butanol extraction procedure. No association between DNA adducts and use of specific pesticides was observed.