(1) A modification of the gelatin viscosity method is described for routine use in determining proteolytic activity of duodenal fluid. This method is compared to the Andersen-Early method and to the method of Free-Myers which uses casein as a substrate.
(2) The sensitivity of the gelatin viscosity method is shown in the assay of commercial pancreatic preparation where a dilution of approximately 1/100,000 is within the optimal range of activity. In routine assay of duodenal fluid a 1/3,000 dilution is optimal.
(3) In a study of duodenal fluid from 3 groups of patients, the results with 3 methods; the viscosity method, the Andersen-Early method, and the Free-Myers modification of the Anson method, are compared. These 3 methods are in agreement when there is practically complete loss of pancreatic function. However, in patients with partial pancreatic insufficiency the Andersen-Early method is not sufficiently quantitative to detect these changes. It is pointed out that approximately 85 per cent of the substrate is used up before any change in activity is detected by the Andersen-Early method.
(4) The gelatin viscosity method and the Free-Myers method are sufficiently quantitative as a measure of proteolytic activity, although there are occasional discrepancies between measurements by these methods which are presumably due to the relative concentration of trypsin and chymotrypsin in the duodenal fluid.