The induction by diethylsulphate of micronuclei derived from acentric fragments or from whole chromosomes was studied in Chinese hamster V79 cells using autoantibodies from the serum of a scleroderma patient (CREST-syndrome) to detect centromere--kinetochore structures. Centromere-containing micronuclei appeared early after treatment and plateaued both earlier and at lower level than centromere-lacking micronuclei. The frequency of centromere-containing micronuclei was in good agreement with that of mitotic chromosome displacement, suggesting that a high proportion of displaced chromosomes were transmitted to the cytoplasm of one of the two daughter cells, where they gave rise to micronuclei. On the contrary, centromere-lacking micronuclei were more frequent than what could be expected from chromosome fragments observed in mitotic stages.