Immunohistochemistry was used to characterize central neurons which react to antibodies raised against neuropeptides known to control reproduction in other molluscs. Antibodies raised against αCDCP (α caudodorsal cell peptide) and CDCH (caudodorsal cell hormone), peptides which control ovulation in the pulmonate gastropodLymnaea, labelled numerous neurons inMytilus, MyaandPlacopecten.The labelled neurons in the cerebral and visceral ganglia ofMytilusare consistent with descriptions of neurons implicated in the control of reproduction on the bases of earlier neurosecretory staining procedures. This study thus suggests that related peptides might be involved in the reproduction of gastropods and bivalve molluscs. The use of selective immunological markers for peptides which might control bivalve reproduction not only permits the tentative identification of neurosecretory cells in bivalves but also suggests a promising avenue for future research aimed at isolating and characterizing neuropeptides involved in the control of reproduction in these molluscs.