Female specimen of the ragworm, Nereis succinea, employs a tetra-peptide, cysteinyl-glutathione (CSSG) as mate recognition and gamete release pheromone during reproduction. In the present study we review the role of peptide-based pheromones in Nereid worms focusing on pheromone production in females. New results demonstrate that the female ragworms produce the pheromone in the course of the oocyte maturation directly correlated to the oocyte diameter. Nevertheless, CSSG production is significantly increasing during the reproductive process, the nuptial dance, itself. The concentrations of the pheromone, nereithione (CSSG) and those of the possible precursors, reduced glutathione (GSH) and oxidized glutathione (GSSG), in the coelomic fluid were determined by HPLC showing that during spawning the female worms excrete 68.5 +/- 12.5 microg/h of the pheromone. GSH is mobilized, or synthesized and continuously converted into the pheromone enabling female N. succinea to maintain a constant level of pheromone release until the GSH reserves are depleted. Upon release CSSG induces not only gamete release in males but in doses as low as 10(-8) to 10(-9) M also significantly increases male swimming activity and as such may guide males towards the slower swimming females.