In the present study we analysed the possible effect of age, sex and smoking on the mean values of micronucleus (MN) and sister chromatid exchange (SCE) frequencies on peripheral blood obtained from 38 subjects ranging in age from 16 to 63 years and 16 centenarians. The mean number of binucleated cells with micronuclei varied in function of age and sex (as demonstrated by the analysis of covariance (F = 13.13; P 0.05). Sex (F = 4.18;P 0.05). The age-associated increase of sex chromosome loss was studied using fluorescence in situ hybridisation (FISH) on interphase nuclei. The loss of Y signals was observed in ∼10% of interphase cells from the centenarians males, that is six times more often than in the younger control men (∼1.6%). The frequency of X signal loss (∼1.7%) in young women was similar to that observed in male controls of the same age but the incidence of the X chromosome aneuploidy in centenarian females was appreciably higher (∼22%) than that found for the Y chromosome in males. These results were correlated with the data on MN formation and a positive correlation between the percentage of aneuploid cells (FISH) and MN values was observed (r = 0.50;P