The peptide products insoluble in 12 % TCA collected in the proximal duodenum of calves at different times after ingestion of milk, skim-milk or whey were characterized by polyacrylamide gel electrophoresis, isoelectric focusing and SDS-pore gradient gel electrophoresis. # -Lactoglobulin anda-lactalbumin were determined by rocket immunoelectrophoresis. The presence of fat did not modify the hydrolysis of milk proteins. Casein coagulation occurred very quickly and the peptides derived from

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... s, which arrived slowly in the gut, reflected a fairly high proteolysis. The presence of casein in the diet did not modify gastric proteolysis of whey proteins. The fl.-lactoglobulin was degraded poorly or not at all, and a -lactalbumin was slowly but completely hydrolized in peptides which had lost their immunoreactive properties. Introduction.