Free D-aspartate (D-Asp) has been previously found in the nervous system of Octopus vulgaris (Mollusca: Cepalopoda) and has recently also been found in many endocrine tissues of the rat. The present study examined whether this enantiomer also occurs in the reproductive system and the brain of the octopus. In this mollusk, D-aspartate was present in both the male and the female reproductive systems. In males, it was found at high concentrations in the prostate, vas deferens, Needham's sac, and testis. In females, a high concentration was found in the oviduct, accessory nidamental gland, and ovary. The concentration varied between 0.4 and 2.9 mumol/g wet tissue, which corresponds to a percentage of D-Asp/total D+L-Asp between 7 and 33%. No appreciable quantities of D-Asp were found in the digestive, excretory, circulatory, and muscular systems, indicating that in the octopus this enantiomer may play a role in both the nervous and the reproductive systems.