Purpose: We looked for differences in mRNA expression between male and female mouse IacTimal glands. Methods: Poly(A)' RNA was isolated from male and female Swiss Webster mouse lacrimal glands. The RNA was reverse trancscribed, and the cDNA was PCR amplified with defined sets of primers for differential display analysis. The products were electrophoresed in polyacrylamide gels and silver stained. A 400 base pair male-specitic product (W9m4) was excised from the gel, re-amplified, subcloned and sequenced. The predicted amino acid sequence of W9m4 was compared with those in NIH data bases using BLASTx. A nylon RNA blot of poly(A)* RNA from male and female mouse tissues (harderian gland, lacrimal gland, submandibular gland, sublingual gland, parotid gland, and liver) was hybridized individually to 32P-labeled clone W9m4, a-actin, and a mouse clone Y3m3 (GenBank accession n AF008595). Y3m3 is related to Fel dI chain 1, a member of the uteroglobin family. Results: The predicted amino acid sequence of mouse W9m4 (GenBank accession #AF272g44) is 31% identical to the N-terminal two thirds of the secreted form of Fel dI chain 2. W9m4 likely encoded a mouse homologue of cat Fel dI chain 2. W9m4 hybridized intensely to a 500 base pair band in an RNA blot of male and female submandibular gland and male lacrimal gland. W9m4 hybridized weakly to a 500 i base pair band in male and female sublingual gland, female lacrimal gland, male harderian gland and male parotid gland. W9m4 did not hybridize delectably to female mouse harderian or parotid gland RNA. W9m4 also hybridized to a 2.2 kb band in male mouse lacrimal gland. Y3m3 hybridized to a 440 base pair band in male and female lacrimal and submandibular glands (heavier in lacrimal gland), and to a weaker 1.5 kb band in lacrimal gland. Hybridization of the blot with an a-actin probe indicated that the RNA was intact and the lanes were equivalently loaded. Conclusions: Fel dI (a multimer composed of chains 1 and 2) is the major allergen of the domestic cat. A mouse homologue of Fel dI chain 2 was expressed strongly in male mouse lacrimal gland, but barely detectable in female mouse lacrimal gland. In contrast, mouse Fel dI chain 1-related mRNA was expressed equivalently in male and female mouse glands.