Abstract:A novel dipeptide, (β‐aspartylglycine (β‐DG), has been isolated from tissues of the marine gastropod molluscAplysia californica.This compound was detected only inAplysiaand not in other molluscs, such asHelixorMercenaria, or in lobster or frog. Among theAplysiatissues, the highest levels of β‐DG were in nervous tissue and in the reproductive tract. β‐DG was assayed by HPLC as theo‐phthaldialdehyde derivative and found to be present in all individual, identified neurons at a concentration of approximately 40 pmol/μg protein. The peptide was identified as β‐DG by gas chromatography‐mass spectrometry (GCMS) using trimethylsilyl derivatives prepared before and after acid hydrolysis. It was further characterized as the β‐isomer by TLC, including Rf, atypical blue‐gray color with ninhydrin, and a violet color with Cu2+‐ninhydrin. A fractionation scheme is described whereby acid‐soluble tissue constituents can be divided into acidic, neutral, and basic components using mini ion‐exchange columns. This partial purification prior to TLC analysis was necessary to remove compounds that interfe