Keratins are intermediate filaments of the cytoskeleton of epithelial cells. They express themselves in simple (Ks. 7, 8, 18, 19 y 20) or stratitified epithelia (Ks. 1, 2, 5, 9, 10, 11, 16). The different expression of these multigenic cytoskeletal proteins is related to cell specific differentiation programs (OSBORN & WEBER, 1983; NAGLE, 1988); For these reasons the analysis of keratins are very relevant for the study of new aspects of histology, histopathology and developmental biology. Moreover, evaluation of keratins by immunofluorescent or immunohistochemistry is useful for the proper identification and characterization of normal, displasic and neoplasic cells (OSBORN & WEBER, 1983; NAGLE). The different patterns of expression of keratins are related to the degree of differentiation of inmature epithelial cells, as well as the degree of differentiation of malignant tumours (FUCHS & GREEN, 1980; FRANKE et al., 1981b; MOLL et al, 1892a; SCHAAFSMA & RAMAEKERS, 1994). Lastly, evaluation of the changes of immunoexpresion of keratins is useful for the differential diagnosis between typical and atypical squamous metaplasia, including moderate and severe epithelial displasia and intraepithelial neoplasia -formerly known as carcinoma in situ- (MOLL et al., 1982a; TSENG et al., 1982; QUINLAN et al., 1985; HUSZAR et al., 1986; GIGI-LEITNER et al; HEID et al.,1988)