Vincristine is an alkaloid widely used as an antineoplastic agent. In eukaryotic cells the drug causes blockage in the G2 phase of the cell cycle and an increase in the frequency of sister chromatid exchanges. Due to the fact that germinating Aspergillus nidulans cells spend most of their cycle in G2 phase, they provide an excellent system for the study of mitotic crossing-over. Taking into account that mitotic crossing-over occurs during G2 period, the evaluation of recombinagenic and aneugenic potential of vincristine is provided with regard to two diploid strains of A. nidulans: a wild strain (uvsH+//uvsH+) and a defective one in DNA repair (uvsH//uvsH). Drug toxicity and its effect on the asexual cycle of A. nidulans has been evaluated as well. Treatment of both strains with vincristine did not change colony growth in the culture, however cytological analyses showed aberrant conidiophores. Recombinagenic potential of vincristine was evaluated by induction of gene homozygosis originally present in heterozygosity diploid strains (Homozygotization Index). Results show that vincristine induces mitotic crossing-over and higher frequency of aneuploid mitotic segregants. The results also show the recombinagenic and aneuploidogenic potential of vincristine and suggest its participation in the induction of secondary malignancies