Localization of amino acid transport sites within the integument of Glycera dibranchiata Ehlers was carried out by freeze-section and freeze-dry histological techniques. The worms were exposed for one hour to the non-metabolizable amino acid analog c(14)-cycloleucine in seawater. Freeze-sectioning and freeze drying of tissue samples allows the localization of water soluble compounds by autoradiography. Amino acid uptake is largely across the parapodial gill surfaces and the epidermis. The gills become rapidly labelled with c(14)-cycloleucine to a greater extent than the epidermal cell layers. Coelomocytes within the gills become radiolabeled in one hour. It is suggested that the rapid labelling of the coelomoctes is due to the close proximity of the cells to the external seawater medium at the parapodial surface, and that the coelomocytes may function to rapidly transfer amino acids to sites of metabolic utilization. Incorporation of exogenously supplied c(14)-proline into various tissues at two, four and seven day intervals was determined by standard histological techniques. Proline is incorporated into the epidermal cell layers as well as the coelomocytes within two days. The circular muscles and longitudinal muscles of the worms become labeled only after four and seven days, respectively.