Electrophoretic and activity variants for a testosterone-induced esteroprotease have been discovered in submaxillary glands from inbred strains of mice. The enzyme is tentatively designated tamase (TAM-I) and the variant genetic locus is Tam-I. The alleles Tam-In and Tam-Ib determine electrophoretically distinct zones of tamase activity, while Tam-IC produces no detectable enzyme activity. Data from recombinant inbred strains and BGAF, x B6 and B6D2F1 x B6 backcrosses established linkage of Tam-I to glucose phosphate isomerase (Gpi-I), pink-eyed dilution ( p ) and /3-hemoglobin (Hbb) on chromosome 7. The gene order is Gpi-I-Tam-l-p-Hbb. Analysis of congenic resistant strains indicates that Tam-I is closely linked to the minor histocompatibility locus, H-4. TAM-I was not cross-reactive with antisera to mouse nerve growth factor, submaxillary renin, or tamases A ancl D. HE submaxillary (submandibular) gland of the male mouse (Mus musculus) Tundergoes extensive, androgeii-dependent developmental changes concomitant with the sexual maturation of the animal (LACASSAGNE 1940; JUNQUIERA Qt al. 1949). This sexual dimorphism is evident histologically by hypertrophy of the epithelial cells lining the secretory tubules ( LACASSAGNE 1940) and reflects the increased secretory activity of these cells (KAIHO, NAKAMURA and KUMEGAWA 1975). Among the products of the submaxillary glands of mature male mice are several trypsin-like proteases (E.C.3.4.4.-) that are capable of hydrolyzing various amides and esters of arginine (LBVY, FISHMAN and SCHENKEIN 1970). These enzymes are collectively designated as tamases because they are assayed with the synthetic substrate, p-tosyl-L-arginine methyl ester (TAMe) . Tamases are absent or present at low levels in the submaxillary glands of virgin adult female and prepuberal male mice, but the enzymes can be rapidly induced in these This research was performed while the author was a Postdoctoral Trainee at the Jackson Laboratory, supported by Public Health Service Training Grant GM 02215. Additional support was provided by Public Health Service Grant GM 18684, National Science Foundation Grant BMS-75-03397 and Contract ES-4-2159 with the National Institute of Environmental Health Services. The Jackson Laboratory is fully accredited by the American Association for Accreditation of Laboratory Animal Care. ’ Present address: Division of Biology, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37830. Genetics 90: 713-724 December, 1978.