Amylase activity in different pH ranging from 3·6 to 8·0 and activity of sucrose, maltose, trehalase, raffinase, lactase, glycogenase, pectinase, chitinase, carboxy methyl cellulase and cellulase at their respective optimum pH were quantitatively estimated in the crystalline style of intertidal bivalves,Crassostrea madrasensis, Meretrix meretrix, Meretrix casta, Katelysia opima andDonax cuneatus. Amylase was the most active among all enzymes tested. A maximum activity of 137·5 μg/mg/h was recorded in the style ofKatelysia opima while the activity was minimal inDonax cuneatus (39·3 μg/mg/h). Two pH optima were recorded for style amylase ofCrassostrea madrasensis (6·0 and 6·8) andKatelysia opima (5·6 and 6·8). But the activity was higher at higher optimum pH. The enzymes hydrolysing oligosaccharides were weak in most cases or absent. The enzymes acting on reserve polysaccharides such as amylase and glycogenase showed maximum activity in the species tested. However the activity of enzymes degrading structural polysaccharides such as cellulase, carboxy methyl cellulase, pectinase and chitinase was either at a low level or absent. The role of the style enzymes in the extracellular digestion of bivalves is discussed.