Some epidemiological and experimental studies showed that there is a relation between estrogen and development of some cancers. The carcinogenicity of estrogens is considered to be the result of a combination of DNA damage by reactive metabolites and indirect genotoxicity by redox cycling and production of reactive oxygen species. Cytokinesis-block mikronucleus test (CBMN) in human peripheral blood lymphocytes has been accepted by many laboratories all over the world as a standard cytogenetic test for genetic toxicology testing. The objective of the present study was to evaluate possible genotoxic effects of estradiol (E2) in cultured lymphocytes, using the CBMN assay. This study was performed in human peripheral blood lymphocytes from a group of 50 healthy men.. No statistically significant difference in micronucleus frequency was detected in E2 (36 µM) treatment (1-11 MN/1000 cells) cultures compared to control (1-15 MN/1000 cells) cultures (p>0.05). The frequency of MN in binucleate lymphocytes was not altered by E2 treatment (5.88±2.9 in control cultures and 5.64±2.5 in treatment cultures; P>0.005). Our results suggest that there are not any genotoxic effects of estradiol in cultured lymphocytes