1. Feeding response exhibition in five marine crustaceans was observed in the presence of a range of concentrations of an amino acid mixture composed of equal parts DL alpha arnino-n-butyric acid, L-glutamic acid and taurine. Gnathophausiaingens, Pleuroncodes planipes, and Cancer antennarius displayed behavioral thresh olds of between 10-10 and 10-12 M; Spirontocaris taylori and Pagurus hirsutiusculus displayed thresholds between 10-7 and 10-9 M. 2. Electrophysiological response thresholds to the amino acid mixture were examined in G. ingens and C. antennarius. The antennular and dactyl receptors of G. ingens displayed thresholds of 10-7 and 10-8 M respectively. Maxilliped and dactyl receptors of C. antennarius both displayed a threshold of 5 x 10-5 M. 3. Panulirus interruptus antennule receptors displayed a degree of specificity to mono- and dicarboxylic amino acids.