Mouse major urinary proteins (MUPs) are encoded by a family of about 35 to 40 highly conserved genes. In the preceding paper (K. Shahan, M. Gilmartin, and E. Derman, Mol. Cell. Biol. 7:1938-1946, 1987), we presented the sequences of the most abundant MUP mRNAs in the liver (MUP I, II, and III) and in the lachrymal (MUP IV) and submaxillary (MUP V) glands. We have shown that these five mRNAs are coded by five distinct genes, MUP I through V. In the present communication, we examine the expression of MUP genes in all of the six tissues in which MUP mRNAs are synthesized, the mammary, parotid, sublingual, lachrymal, and submaxillary glands and the liver. We show that gene MUP II is expressed in the liver and in the mammary gland, that gene MUP IV is expressed in the lachrymal and parotid glands, and that gene MUP V is expressed in the submaxillary, sublingual, and lachrymal and parotid glands, and that gene MUP V is expressed in the submaxillary, sublingual, and lachrymal glands. Furthermore, we present evidence that in addition to genes MUP I through V, another gene, MUP VI, is expressed in BALB/c mice in the parotid gland. The tissue-specific synthesis of MUP mRNAs is thus brought about by two major mechanisms: the expression, in different tissues, of different members of the family and the expression of a single gene at various levels in different tissues. When a particular MUP gene is expressed in several tissues, transcripts of this gene initiate at the same site and are spliced and polyadenylated in the same manner.