"Levamisol" is an antiparasitic drug produced by ICN-Galenika (Yugoslavia). This anthelmintic was cytogenetically analyzed in vivo in an experiment on three groups of Wistar rats. The control group of rats was treated with saline. Experimental animals were injected intraperitoneally with two therapeutic doses of the anthelmintic (2,2 mg levamisole hydrochloride/kg b. w. and 4,4 mg levamisole hydrochloride/kg b.w.) during a seven day treatment period. Cytogenetic changes of bone marrow cells were evaluated by determination of their mitotic index, as well as structural and numerical chromosomal aberrations. Both tested doses of the anthelmintic induced an increase of mitotic index, aneuploidy, polyploidy and structural chromosomal changes of the break and insertion type of lesion. Insertions were observed on the first pair of autosomes.