In hematoxylin and eosin (H and E) stained sections from liver biopsies, the destruction of bile ducts in the portal triads is regarded as an important histologic parameter in the diagnosis of primary biliary cirrhosis (PBC). In contrast, the bile ducts are not destroyed by chronic inflammation in chronic active hepatitis (CAH). Nevertheless, the differential histologic diagnosis between PBC and virus or autoinmune-induced chronic active hepatitis (CAH), is very difficult in 15% of cases. That difficulty is mainly due to the impossibility of identifying bile ducts in the portal triads with marked lymphocytic infiltration. In this investigation we report that bile ducts may be specifically stained by anti-human cytokeratin 7 (CK7). Sections from 16 liver biopsies (PBC = 6, CAH = 6 and fatty liver (FL) = 4) were stained with H and E and CK7. The results in H and E stained sections indicated that the mean number of bile ducts found in PBC was was 0.56 (range 0-2), in CAH 0.67 (range 1-3), and in FL 0.56 (range 1-3). In parallel CK7 stained sections, the mean number of bile ducts in PBC was 5.33 (range 2-35), in CAH 3.44 (range 4-18), and in FL 1.39 (range 2-6). The difference between H and E and CK7 stained sections was significant (p < 0.001) in all 3 groups. In the light of these preliminary results, it would appear that Cytokeratin 7 may be the stain of choice to detect bile ducts, an important parameter to histologically differentiate between PBC and CAH, as well as to classify PBC into its different stages.