Chemoreception in the adults of the freshwater prawnMacrobrachium rosenbergii was investigated under controlled laboratory conditions, using behavioral assays. Tests were carried out on groups, as well as on individuals, all at their intermolt stages of the molt cycle, and prestarved for three to four days. Of 28 different substances tested, the amino acids taurine, glycine, arginine, and betaine, as well as trimethylamine, elicited a positive behavioral response in at least 50% of the test animals when applied at a threshold concentration of 10(-5)-10(-8) M. A positive response comprises enhanced antennular flicking and food search motion. Of the various nucleotides tested for chemoattraction, only adenosine monophosphate elicited a response similar to that of the above amino acids, although at a concentration of 10(-4) M, whereas adenosine diphosphate required a dosage of 10(-1) M.