Spontaneous baseline frequencies of chromosome aberrations, micronucleus counts and cell division were analysed in peripheral lymphocytes of 127 normal healthy individuals in vitro. Cells were subjected to culture for 48 h in serum and PHA supplemented culture medium RPMI 1640. 100 metaphases were observed for chromosome aberrations and 1000 cells each for micronucleus counts and mitotic index. Regression analyses were carried out to see the effect of age on spontaneous abnormalities. The correlation of aberrations, micronucleus formation and mitotic index with donor's age is highly significant. The elevation of abnormalities and depression of mitotic index were linear to the increase of donor's age, with a higher frequency in males. Aged males and females from the age range of 40-70 years showed larger numbers of aberrations. Individuals with the smoking habit possessed higher frequencies of abnormalities than non-smokers.