Although mammalian pheromones have been stud-ied for almost five decades, the genetic control of theirphysiological activity is still poorly understood. Thisproblem remains one of the most intricate in this newinterdisciplinary field of biology.Considerable polymorphism of the activities ofandrogen-dependent pheromones has been found indifferent mouse strains [1–3]. This has created a meth-odological basis for genetic studies aimed at revealingthe key molecular and biochemical mechanismsresponsible for the biogenesis, metabolism, and releaseof pheromones. Genetic models are promising tools forexperimental studies on the biochemical basis of theregulation of the pheromone physiological activity [4].According to one of the most promising moleculargenetic models [5], the physiological activities ofandrogen-dependent pheromones of the house mouse( Mus musculus L.), including 2- sec -butyldihydrothia-zol and 2, 3-dehydro- exo -brevicomin, are related to thelevel of a protein belonging to the major urinary protein(MUP) complex, which is excreted with urine. Individ-ual Mup genes mapped to chromosome 4 [6] have beenfound to control the biosynthesis and differentialexpression of certain androgen-dependent MUP frac-tions. The available data allow researchers to addressthe problem of the role of these genes in the regulationof the physiological activity of pheromones.The purpose of this study was to detect and analyzethe testosterone-induced expression of the Mup genecomplex in laboratory strains of mice with hereditarydifferences in the activities of androgen-dependentpheromones.We used male and female CBA/LacY andC57BL/6JY mice and their reciprocal F1 hybrids ( N =162). In experiments with changed endogenous test-osterone concentration, six-week-old males were cas-trated using the standard technique with ether anesthe-sia [3]. When castrated animals were eight weeks old,capsules (Dow Corning, United States) containingcrystalline testosterone propionate (TP) (Sigma, UnitedStates) were implanted into some of them. The capsuleswere implanted near the nape of animals anesthetizedwith ether; control animals were implanted capsuleswithout TP. The working part of the capsule was 10 mmin length, which corresponded to a daily TP dose of27.1 µ g [6].The total protein concentration in urine was deter-mined according to Bradford. The endogenous β -glu-curonidase (EC 3.2.1.31) was estimated by the standardFischmann’s phenolphthalein method. The plasma con-centration of testosterone was estimated by radioimmu-noassay using standard kits (Sorin, France). MUP pro-teins were fractionated by means of nondenaturing ver-tical gel electrophoresis in a tris-acetate buffer system(pH 5.5) [7]. Gel plates were scanned using a GelScanXL laser densitometer (Pharmacia, Sweden).The data obtained are shown in Figs. 1, 2 andTables 1, 2. The main results are summarized below.(1) Eight electrophoretic fractions (A–H) may bedistinguished in the MUP complexes of CBA andC57BL/6 mice. Fractions A, B, C, D, G, and H werecharacteristic of both strains. Fractions E and F wereunique; they may serve as phenotypic markers of theCBA (fraction E) and C57BL/6 (fraction F) strains.Castrated CBA males lacked fractions B and C, andcastrated C57BL/6 males, fraction D (Table 1). Castra-tion caused a decrease in the concentrations of individ-ual fractions of the MUP pool, except for the majorfraction E in CBA mice. Replacement testosteronetherapy recovered the MUP polymorphism to the levelobserved in animals subjected to false castration. Theadministration of TP caused a proportional increase inthe concentrations of all MUP fractions: in each strain,the coefficient of rank correlation between concentra-tions of individual protein fractions in variants I and IIIwas 1.(2) The content of MUP fractions constantlyincreased in the course of ontogeny in males of both