The free amino acids and other related substances of 17 species of aquatic invertebrates were studied chromatographically. Different patterns of distribution are shown but the differences cannot be correlated with the environment alone. Taurine was found in all the marine organisms but it was absent from a number of fresh water and terrestrial organisms. Of interest is the presence of [beta]-alanine and [beta]-amino-isobutyric acid in some of the organisms studied.