Pattern formation in the Drosophila embryo requires the concerted expression of maternal and zygotic genes. At least nineteen genes, twelve of which are maternally expressed, are involved in the establishment of dorsal-ventral polarity. Mutations in any one of these genes result in distinct alterations of cell fates and in the formation of an abnormal dorsal-ventral pattern. Mutants of the 'dorsal group', eleven of the maternal genes, have a common recessive phenotype similar to that described for dorsal, in that cells located at ventral and lateral positions assume dorsal fates and ventral structures fail to develop. Thus the dorsal group gene products may be involved in the establishment of a gradient of positional information along the dorsal-ventral axis. We have cloned snail (sna), a zygotic gene, whose expression is essential for the correct specification of dorsal-ventral pattern. In this report, we present evidence that the complementary DNA-deduced protein product of sna contains five copies of a nucleic acid-binding finger motif previously identified in two transcription factors, and in the protein product of several putative regulatory genes.