Doxorubicin is a benzanthroquinone drug which is widely used in the treatment of human malignancies. It acts by interacting with nuclear topoizomeraze II and produces an increase in the DNA strand breakes. Studies performed in vivo and in vitro on different cell lines showed an increase in the frecvency of micronuclei. In this study we analized the effect of low doses of doxorubicin on micronucleus formation on human lymphocytes cell cultures. Cell cultures from a healthy non- smoker donor were treated with increasing doses of doxorubicin as follows: 0.025microM, 0.05microM, 0.1microM 0.25microM. Doxorubicin was added after 48 hours and the cultures were harvested after 24, 96 and 120 after. The slides were stained Giemsa. Micronuclei were scored in a total of 500 mononucleated cells. An increase in the MN formation was noticed with dose increasing and time of exposure. At 120 hours the highest MN formation rate was noticed - 16 MN/500 mononucleated cells at 0.1microM.The lowest rate was for 0.025M after 24 hours. The results are similar to those reported in other studies.