Recently, a new class of homeodomain containing proteins, pbx1, pbx2, and pbx3 has been described. pbx proteins are most closely related to two yeast regulatory proteins, a1 and alpha 2. Here, we identify and characterize the pbx homolog in Drosophila, designated Dpbx. Dpbx is 95% identical to the pbx proteins within the homeodomain and, more remarkably, is 85% to 88% identical within a 201 amino acid region adjacent to the homeodomain. Cytologically, the Dpbx gene is located on the X chromosome at 14A. mRNA expression is both maternal and zygotic and occurs throughout the life cycle. Prior to full germband retraction, Dpbx is rather ubiquitously present and variations are minor. The most notable feature of Dpbx expression is that after germband retraction, high levels of Dpbx are observed in the anterior portion of the ventral nerve cord.