In the early 1980s both our group (Hansbrough & Garbers, 1981; Garberset al., 1982) and that of Norio Suzuki (Suzukiet al., 1981) identified the active material in sea urchin egg conditioned media that could stimulate sperm motility and metabolism. In the sea urchinsHemicentrotus pulcherrimusorStrongylocentrotus purpuratus, the active material was a small peptide that we named speract, and the Suzuki group named this and subsequent peptides SAPs, for sperm activating peptides. Subsequently, both groups identified other peptides (see Suzuki & Yoshino, 1992 for review), one of the most interesting being one named resact, the active material inArbacia punctulataegg conditioned media. This peptide turned out to be the first animal sperm chemoattractant identified (Wardet al., 1985a). A peptide also turned out to be the active principle that explained previous observations of Ward and Vacquier (Wardet al., 1985b; Suzukiet al., 1984) that egg conditioned media could cause the rapid dephosphorylation of a major membrane protein of spermatozoa. The apparent receptor for resact was later identified as a guanylyl cyclase, establishing a new paradigm for low-molecular-weight second messenger signalling, and the major phosphoprotein regulated by resact was also the receptor itself.