In Drosophila melanogaster the small bristles (sbr) gene is vital and evolutionary conservative and controls nuclear export of mRNA. Sbr mutant alleles had a broad pleiotropic effect. High frequency of abnormal larva dying (up to 18 %) at the first instar stage in progeny of heat shock (37 degrees C, 1 h) treated mutant females is one of the most interesting l(l)ts403(sbr10) allele effects. Abnormal larvae display characteristic phenotype that involves the Malpighian tubules defect. Using interphase FISH method (fluorescence in situ hybridization), we showed that abnormal larvae had monosomy on chromosomes 2 and 3. DNA content in neuroblast interphase nuclei of abnormal larvae is 2.1 times less than in normal larvae. We suggest that abnormal larvae could be full or mosaic haploids that appeared as a result of maternal genome loss during fertilization or the mitotic division. Larvae with the same abnormalities appear in a progeny of females with different genotypes mating with males carrying compound chromosomes 2 or 3. FISH analysis showed that such larvae had monosomy only on a chromosome that is compound in paternal strain. Thus, monosomy on large autosomes may cause aspecial phenotype of abnormal larvae in D. melanogaster.