Serum lipase is determined by following turbidity changes during two 1-min intervals after adding serum to an olive oil emulsion containing desoxycholate. The olive oil emulsion is simply prepared and is stable for a month under refrigeration. Our observations confirm the findings of other investigators that increases in serum lipase activity are more accentuated than increases in serum amylase activity during pancreatitis. With the present fast and convenient method, serum lipase appears to be a better test for pancreatitis than is serum amylase.