Aneugenic effects of the Vinca alkaloid vinorelbine (VRB) were evaluated in vitro, measuring sister chromatid exchanges (SCE), cell proliferation kinetics and anaphase telophase aberrations in Chinese hamster ovary (CHO) cells. The highest dose of VRB (0.50 microg/ml) arrested cells at the first metaphase. An increase in abnormal anaphases was seen at 0.05-0.50 microg/ml of VRB, containing chiefly lagging chromosomes and multipolar spindles. No increase in SCE was found. These results indicate that VRB does not directly damage DNA, but acts on spindle microtubules, altering chromosome movement and causing aneuploidy.