This study examined differential expression of several mucin genes in the human submandibular gland and trachea, MUC7 tissue and species specificity, and MUC7 genetic polymorphism. Mucin gene expression examined by RT-PCR indicated that MUC1, MUC4 and MUC7 are expressed in the human submandibular gland, while MUC1, MUC2, MUC4, MUC5 and MUC7 are expressed in the human trachea. Northern blot analysis confirmed the expression of MUC7 in the human trachea and MUC4 in the human submandibular gland. Northern blot analysis also demonstrated that MUC7 is not expressed in the submandibular/sublingual gland complexes of hamster, mouse and rat. Southern blot analysis suggested the presence of a MUC7 homologue in monkey genomic DNA. Genetic polymorphism studies of MUC7 by PCR and Southern blot analysis revealed the presence of a limited variable number of tandem repeats (VNTR) polymorphism. Abbreviations: RT-PCR, reverse transcriptase polymerase chain reaction; DNA, deoxyribonucleic acid; RNA, ribonucleic acid; ORF, open reading frame; VNTR, variable number of tandem repeats; HSMSL, human submandibular-sublingual saliva; MG1, high molecular weight mucin glocoprotein; MG2, low molecular weight mucin glycoprotein; SDS, sodium dodecyl sulfate; NBT, nitro blue tetrazolium; BCIP, 5-bromo-4-chloro-3-indolyl phosphate; Na2EDTA, disodium ethylenediamine tetra-acetic acid; dGTP, 2′-deoxyguanosine-5′-triphosphate; dCTP, 2′-deoxycytidine-5′-triphosphate; dATP, 2′-deoxyadenosine-5′-triphosphate; dTTP, 2′-deoxythymidine-5′-triphosphate; TE buffer, (10 mM Tris-HCl, 1 mM Na2EDTA, pH 8.0); RE, restriction endonuclease.