1. Specimens of Asterias forbesi, Henricia sanguinolenta. and Echinaster spinulosus were exposed up to 24 hours to sea water media containing C14-labeled amino acids. The distribution of the labeled compounds after periods of 1 hour to 21 days was determined by means of stripping-film autoradiographs of histological sections of the specimens. 2. The results from all three species were very similar. Large quantities of the supplied amino acids were found to have been taken up and retained by the epidermal cells in almost all regions of the body, and especially in those parts most in contact with the external medium. Variations in uptake between the different types of cells making up the epidermal layer appeared to be only minor and relative. 3. The amino acids were found not to have penetrated through the madreporite channels or through the buccal opening. If fluid entered these regions, the amino acids were presumably completely removed by the adjacent superficial cells, which always demonstrated large amounts of uptake. 4. Secretions by the large epidermal glands characteristic of Henricia and Echinaster appeared to contain at least some material derived from the exogenous amino acids supplied. 5. There was very little evidence of movement of the absorbed amino acid out of the epidermal cells within the 3-week period during which the observations were continued. Only slight translocation occurred in some of the tube feet and in the region of the radial nerve cord. 6. It is concluded that absorption of environmental amino acids (and probably other compounds) by the epidermis is an important and often principal source of nutrition for the cells making up this tissue; other areas of the body, however, depend almost exclusively on endogenous sources of nutritive substances, probably delivered by the fluids circulating through the various body cavities.