The bag cell neurons of Aplysia californica synthesize and store large amounts of peptides derived from the egg-laying-hormone (ELH) neuropeptide precursor. Different sets of peptides derived from the amino- and carboxyl-terminal regions of the prohormone possess unique biological activities, and are packaged in distinct sets of secretory granules. We report here quantitative measurements of the amounts of the peptide products stored in and released from the bag cell neurons using high pressure liquid chromatography (HPLC) and amino acid composition analysis. These studies demonstrate that both the autocrine acting bag cell peptides (BCPs) and ELH are released coincident with electrical activity in the bag cell cluster. The composition of the released peptide mixture is similar to that stored in the bag cells. ELH and other carboxy-terminal derived peptides are most often present at 5-fold greater levels than the BCPs. These results provide further insight into the use of multiple chemical messengers by the bag cell neurons.