This study compared the pattern of keratin expression in pilosebaceous follicles in uninvolved trunk skin of acne patients, comedones, and normal control skin by immunohistochemistry, using both immunofluorescent (IF) and immunoperoxidase (IP) techniques. The shape, size and gross morphology of truncal follicles varied greatly. There was no difference in keratin expression between normal skin and uninvolved skin of patients with acne. The upper part of the pilosebaceous duct expressed keratins K1, K5, K10 and K14, whereas the lower duct expressed keratins K5, K6, K14, K16, K17 and K19. The sebaceous gland showed considerable heterogeneity in keratin expression, with some lobules expressing keratins K1, K5, K7, K10, K14 and K17. The comedone wall showed a pattern of keratin expression similar to that of the upper follicle, except that there was, in addition, expression of keratins K6 and K16 suprabasally, and panepithelial expression of K17 in the comedone wall. IF techniques were found to be less sensitive than the IP method in the detection of individual keratins, but the use of multiple antibodies and many different transverse and longitudinal sections of follicles permitted full conclusions to be made. The increased expression of keratins K6, K16 and K17 in the comedone wall is likely to represent a secondary effect of increased cell turnover due to the primary underlying mechanism of comedogenesis, which is as yet unknown.