A technique is described in which irrigation of the mantle cavity of oysters, Crassostrea gigas, induces pumping at steady rates. Simultaneous net influx of 10 amino acids (asp, glu, asn, ser, gly, tau, ala, val, phe, lys) is observed by high-performance liquid chromatography (HPLC). Individual amino acids exhibit first-order exponential depletion from an initial medium concentration of 2.0 μM. Influx of radiolabeled alanine corresponds very closely to net entry of alanine as estimated by HPLC. Therefore, net entry of alanine from dilute solution (5 μM) occurs. The entry of alanine is well described by Michaelis-Menten kinetics with a maximum influx (Jmax) of 1.76 μmol g−1 h−1 ±0.028 (SD) and a half-saturation constant (Kt) of 33.70 μM ±1.15 (SD). Amino acids taken up from solution are distributed rapidly to the internal tissues of the animal. This is demonstrated for alanine and glutamate and for the amino acid analogues, cycloleucine and α-amino-n-butyric acid (ABA). HPLC analysis of the free amino acid pools of mantle, gill, adductor muscle and hemolymph of C. gigas demonstrates variability in total concentration and in details of FAA composition.