We have discovered a reporter gene insertion that is expressed in the trunk region of Drosophila embryos. Genetic and molecular details of a new regulatory gene neighboring the reporter gene insertion, which we call teashirt (tsh), are described. In situ hybridization of a tsh probe to embryos shows that this gene is expressed in a way similar to the reporter gene. Mutations of tsh show that the gene is required for normal development of the ventral trunk region of embryos, which correlates with the spatial expression of the gene in the anteroposterior axis but not in the dorsoventral axis. Sequencing of a tsh cDNA shows that the putative protein possesses three distantly spaced CX₂CX₁₂HX₅H zinc finger motifs.