In this survey, lipid metabolism and activities of the lipolytic enzymes diglyceride lipase (DLase) and phospholipase A (PLase A) in the oyster digestive glands (ODGs), with 4% added acetic acid (the same acid concentration as vinegar) and incubated at 37 C for 3 h, were investigated. Significant decreases in triglyceride, phosphatidylcholine, and phosphatidylethanolam ine and increases in monoglyceride, lysophosphatidylcholine, and lysophosphatidylethanolamine were observed in the acetic acid-treated ODGs. Changes in ODGs treated with PBS were smaller than in the acetic acid-treated ones but larger than in the nontreated ones. Both PLase A1 and PLase A2 in ODGs were activated by addition of acetic acid and incubated at 37 C for 3 h. PLase A1 activities were higher than those of PLase A2 in all experim ental O DGs. Addition of formic acid also induced activation of PLase A at pH 2. On the other hand, DLase in O DGs decreased rem arkably with acetic acid treatment. These data showed that the increase in lipid metabolites such as free fatty acids and lysophospholipids in the acetic acid-treated ODGs might be due to catabolism of PLase A, which was activated by the acid treatm ent at 37 C.