The Rho GTPases regulate many different cellular and developmental processes, and activation of Rho GTPase signalling is mediated through interaction with the Dbl homology (DH) protein domain. We describe the expression pattern of DrhoGEF3 (cytological position 61B1-B3), which encodes a new member of the DH domain protein family from Drosophila and is a homologue of the human protein hPEM-2. During gastrulation and germ band extension, DrhoGEF3 exhibits a segmented expression pattern. DrhoGEF3 is subsequently expressed in the visceral mesoderm, at the sites of muscle attachment and in specific groups of sub-epidermal cells. The possible function of such a dynamically expressed signalling molecule is discussed.