The small bristles (sbr) gene of Drosophila melanogaster belongs to the family of nuclear export factor (NXF) genes that participate in mRNA nuclear export. The sbr10 (l(1)ts403) thermosensitive allele together with a null allele has a strong sterilizing effect on sbr10 / Df(1)vL4 or sbr10/0 hemizygotic females at a permissive temperature. Early embryonic lethality among offspring distinguishes sbr10/0 females from the females that are heterozygous for other lethal alleles of the sbr gene. Among disruptions detected during early embryonic stages of sbr10/0 female offspring, the most characteristic effects were asynchrony of the first cleavage divisions, changes in the morphology of nuclei, and the appearance of zones without nuclei or, on the other hand, with large chromosome-clusters. Such disruptions allow supposing that sbr gene is involved in the control of early embryonic mitoses.