Mature laboratory male mice CBA, C57BL/6, BALB/c, and hybrids CBAB6F1 were exposed for 2 or 24 h to vapors of 2,5-dimethylpyrazine (DMP), which is a pheromone of the house mouse. This caused changes in the content of noradrenaline within the nerve fibers of both nasal mucosa and vascular testis tunic and an inhibition of leukocyte migration in the peripheral blood. Intrastrain distinctions were also revealed in the level of spontaneous leukocyte migration and the intensity of the response to the DMP. The mechanisms underlying these effects and their possible adaptive significance are discussed.