To examine the role of microfilaments and microtubules in centrosome dynamics we exposed Drosophila embryos to culture medium containing cytochalasin B and to low temperature. The results show that the splitting of the centrosomal material does not occur when the embryos are treated with cytochalasin before centrosome duplication at late telophase. The fragmentation of the centrosomal material, caused by cold exposure, is also prevented by cytochalasin incubation. These results indicate that both microtubules and microfilaments may be involved in determining centrosome shape during the syncytial mitoses which lead to the formation of the blastoderm in early Drosophila embryos.