Zinc-alpha 2-glycoprotein (Zn alpha 2gp) is almost ubiquitous in body fluids, and its antibody labels the corresponding secretory epithelia. We have found that Zn alpha 2gp is also expressed in human epidermis. We cloned the Zn alpha 2gp cDNA by screening our cDNA library, derived from epidermal keratinocytes, with a probe for prostate Zn alpha 2gp. It had complete nucleic acid sequence homology with that from prostate, including the signal peptide. Just as Zn alpha 2gp expression is higher in more differentiated breast tumors, so in skin tumors the highest mRNA levels occurred in the normal controls, the lowest in basal cell carcinomas (the least differentiated epidermal tumor type), and intermediate levels in squamous cell carcinomas and Merkel cell carcinomas. A similar increase in Zn alpha 2gp gene expression with differentiation was observed when epidermal keratinocytes were cultured in media that varied in cellular maturation potential.