Small peptides displaying a cysteine-rich module (termed P-domain or trefoil motif) form a recently increasing group of peptides abundantly expressed at mucosal surfaces of specific tissues and are associated with the maintenance of surface integrity. The estrogen-inducible pS2 gene (BCEI) and the human homolog to the porcine spasmolytic peptide (hsP) gene (SML1) appear synchronously expressed in healthy stomach mucosa and several carcinomas of the gastrointestinal tract. Both genes were shown to be located at 21q22.3. A new trefoil peptide from human intestinal mucosa (hITF/hP1.B) and its gene (TFF3) were described recently. By PCR analysis of a somatic cell hybrid panel and FISH using two large genomic recombinants (110 kb, 210 kb) cloned in the Bacterial Artificial Chromosome (BAC) system, we show that this gene coding for the new member of human P-domain/trefoil peptides also maps to chromosome region 21q22.3 suggesting a physical linkage of all three trefoil peptide genes.