Syrian hamster Harderian glands show a typical sexual dimorphism, with males having two secretory cell types and females having one cell type and intraluminal porphyrin accretions, among other differences. Since these differences may be due to the expression of specific genes, our interest is to identify those genes and their role on the development and control of the sexual dimorphism. The experimental approach was to construct cDNA libraries for male and female Syrian hamster Harderian glands and then subtracted libraries for male vs. female and for female vs. male. By this method, cDNA libraries enriched either in male-specific or in female-specific clones were obtained. Clones from those libraries were checked for differential expression by using double colony hybridization with [32P]-cDNA from male and female glands. Then, the selected clones were checked again for expression in Harderian glands by Northern hybridization, using poly(A+) RNA from males, castrated males, and females. Finally, the clones were sequenced and compared to search for significant homologies. One of the male-specific clones showed strong homology with rat cytochrome p450b/e. Among the female-specific clones, homologies were found to the complement C3 fragment from several species, to sequences from the mouse mammary tumor virus, and to the subunits C1 and C2 of the rat prostatic steroid binding protein. Several other clones showed no significant homologies and need further characterization.