The expression of AE1, AE2, AE3, and CAM 5.2 antikeratin monoclonal antibodies was investigated in 68 vulvar specimens by an avidin-biotin complex (ABC) method. They included normal vulva (NV, 10), non-neoplastic epithelial disorders (NNED, 31), vulvar intraepithelial neoplasia (VIN, 17), and squamous cell carcinoma (SCC, 10). AE1 weakly stained the basal cell layer in NV, exhibited a uniform suprabasal stain in hyperplasia, failed to stain dysplastic areas in VIN I-II, and was patchy and disorganized in VIN III and SCC. AE2 stained the upper third of the epithelium in NV, NNED, and VIN I-II, but it failed to stain VIN III basaloid and SCC; VIN III bowenoid was focally positive. AE3 offered little information, because it stained all lesions; VIN III and SCC, however, exhibited a patchy and disorganized stain. CAM 5.2 was expressed in only half of the cases of VIN III basaloid and in one case each of VIN I-II and SCC. We conclude that keratin expression varies according to the degree of dysplasia; AE1 may serve to separate certain cases of NNED from VIN I-II; AE2 and CAM 5.2 are useful to differentiate both histologic types of VIN III.