We have isolated a hair-follicle-specific gene, termed hacl-1, from a cDNA library of ICR mouse skin. Hacl-1 is expressed specifically in skin, and its mRNA level is correlated with the active state of hair follicles in developmental and regenerative processes of hair. Its mRNA is approximately 1 kilobase pairs (kb). Its cDNA was completely co-linear with the genomic clone, indicating that the hacl-1 gene is composed of one exon. The hacl-1 gene has an open reading frame of 579 base pairs (bp). The deduced amino acid sequence showed six direct repeats of a decapeptide on the C-terminal side. The repetitive unit contains a CQP motif, which is present in repetitive peptide sequences of some hair- and epidermal-cell-specific proteins. In situ hybridization with a 3' untranslated region of the hacl-1 cDNA as a probe showed that hacl-1 was expressed specifically in the keratogenous zone of the cortical cells of the hair shaft. No other components of hair follicles or epidermis showed a positive signal. Thus, hacl-1 is a novel, hair-follicle-specific gene.