Volume 4 of Advances in Developmental Biology and Biochemistry consists of five chapters that review specific aspects of sea urchin, fly, and mammalian development. In Chapter 1, A. Bejsovec and M. Peifer discuss the nature and role of the wingless/Wnt-1 signaling pathway in Drosophila, as well as in amphibia and mammals. In Chapter 2, C. Ettensohn and colleagues discuss cell interactions, cell fate specification, and morphogenesis in sea urchin embryos. In Chapter 3, E. Kubli discusses the nature and role of a Drosophila sex-peptide that serves as a pheromone involved in reproduction. In Chapter 4, T. Gridley discusses the expression and functions of several vertebrate homologs of the neurogenic genes of Drosophila. In Chapter 5, J. Pollard and R. Stanley discuss the pleiotropic roles for colony stimulating factor-1 in development as defined by the mouse mutation osteopetrotic.