A method for determining serum lipase activity requiring only 4 hours incubation at 37° is given. Olive oil in a phosphate buffer is the substrate. The values found in 57 healthy controls ranged between 0.06 and 0.87 units, with a mean of 0.31 ± 0.17 (S.D.). Some results are given for patients with pancreatitis, miscellaneous pathologic conditions, and healthy controls.