We have examined the keratin proteins in normal human oral mucosa from 6 different regions including hard palate, buccal mucosa, tongue, gingiva and floor of the mouth. Urea‐dithiothreitol extracts of EDTA separated epithelia were analysed by SDS‐PAGE and immunoblotting. Eight samples from each region were investigated and showed very little individual variation in the keratin profile on Coomasic Blue‐stained gels. The keratinizing hard palate and gingiva expressed identical patterns and resembled the pattern of epidermis from the flank region. The normally non‐keratinizing buccal mucosa and the mucosa of the floor of the mouth expressed polypeptides distinctly different from those of the keratinizing epithelia and lacked the high molecular weight keratins. The dorsal surface of the tongue and the commissure region showed a pattern intermediate between keratinizing and non‐keratinizing epithelia. The greater sensitivity of the immunoblotting technique revealed that the non‐keratinizing epithelia synthesized one of the high molecular polypeptides and that the tongue produced all the bands found in keratinizing epithelia, but in very small quantities. There are, thus, distinct differences in the keratin expression of oral epithelia which are related to the pattern of keratinization assessed his