Keratin was extracted from human callus with Tris-HCI buffer containing 8M urea and 0.1 M mercaptoethanol. The molecular weight was determined by SDS-PAGE as 46

000

50

000

55

000 and 63

000 daltons. Under negative staining electron microscopy

the keratin was a filament with a diameter of 80-100A. The antikerain antiserum was produced by immunizing keratin in rabbits. It showed a titre of Ii32 by agar diffusion. Its specificity was determined by peroxidase-antiperoxidase method. It reacts with normal epithelium and epithelial tumor tissues

but not with non-epthelial tissues and their tumors. So this antiserum is specific for keratin

and is useful as a reagent in the identification of epthelial tumors