Pulse-chase studies indicate that the peptide egg-laying hormone, ELH, of the neurosecretory bag cells of the mollusk Aplysia is generated by a complex multistep proteolytic processing sequence. Such data indicate that ELH and another secretory peptide, AP (acidic peptide), are generated from a 29,000-dalton precursor via a common intermediate and that this precursor also gives rise to an additional 13,000-14,500-dalton product. In the present study, we have adapted the procedure of Elder et al. [Elder, J. H., Pickett, R. A., Hampton, J., & Lerner, R. A. (1977) J. Biol. Chem. 252, 6510-6515] to obtain tryptic fragments of biosynthetically labeled bag cell proteins. Analyses of these fragments by isoelectric focusing and thin-layer chromatography/electrophoresis are consistent with the processing sequence inferred from pulse-chase data. Furthermore, the peptide maps have revealed the presence of an additional copy of the AP peptide within the 13,000-14,500-dalton product.