HYDROLYTIC ENZYMES OF THE DIGESTIVE TRACT IN CLAMS Ruditapes decussatus AND Ruditapes philippinarum.- The distribution of various hydrolytic enzymes was studied in the digestive tracts of the clams, Ruditapes decussatus and Ruditapes philippindrum. The activity of the enzymes, alkaline phosphatase, acid phosphatase. 5'-nucleotidase, glucose-6-phosphatase and adenosinetriphosphatase was evaluated semiquantitatively in unfixed samples cut by a cryomicrotome at -15ºC. No difference between species was observed in the location of the enzymatic activities. However, there was a variation in the intensity of reaction in the different structures of the digestive tract. Alkaline and acid phosphatase activities were strong in the digestive diverticula, glucose-6-phosphatase showed medium activity in the midgut epithelium, 5'-nucleotidase activity was weak in the gastric epithelium and crystalline style, however the ATPase activity at pH = 9.6 was very intense in the midgut epithelium. Total inhibition of alkaline phosphatase and glucose-6-phosphatase occurred with both L-cysteine (1 mM) and L-phenylalanine (50 mM). N-ethylmaleimide (20 mM) partially inhibited alkaline phosphatase and ATPase activities at pH = 9.6. Acid phosphatase activity was partially inhibited with potassium tartrate (10 mM) and totally with sodium fluoride (10 mM) in the epithelium. All enzymatic activities we investigated were inhibited with (HgCl₂, 1 mM).