The expression of neuropsin mRNA in vivo in mouse skin was examined by in situ hybridization and Northern blotting under stimulated conditions. Two kinds of epidermal stimuli, a topical application of a chemical tumor promoter and incisional wounding, were used. A single topical application of 12-O-tetradecanoyl-phorbol 13-acetate induced epidermal hyperplasia and simultaneously induced an extensive increase in neuropsin mRNA in the suprabasal cells. A full-thickness skin incision also induced a profound increase in neuropsin mRNA in the suprabasal cells surrounding the wound but not in actively proliferating basal cells. The increases in neuropsin mRNA occurred rather late and were limited to the site of drug application or around the incision. Interestingly, neuropsin mRNA was not expressed in the epithelial tongue migrating toward the wound during re-epithelialization. Thus, neuropsin might participate in accelerated epidermal differentiation rather than in the proliferation or migration of keratinocytes in the wound.