Androgens and estrogens exert potent divergent feedback effects on gonadotropin-releasing hormone (GnRH) production at the level of the hypothalamus and GnRH action at the level of the pituitary. Androgens exert generally suppressive effects on GnRH production and action, whereas rising levels of estradiol increase both GnRH release and action. In addition to its known endocrine actions, GnRH possesses immunomodulatory effects. We have previously demonstrated gender differences in immune responsiveness to GnRH that parallel gender differences in endocrine responsiveness: females appear to be more immunologically responsive to GnRH than males. GnRH exerts its actions via the stimulatory G protein Gα<sub>q</sub> and Gα<sub>11</sub> (referred to collectively as Gα<sub>q/11</sub>) as well as via Gα<sub>s</sub>. We have recently demonstrated that the heightened immune responsiveness to GnRH in lupus-prone female mice correlated with increased expression of Gα<sub>q/11</sub> in lymphoid cells from females compared to males. We hypothesize that the hormonal milieu of females may contribute to increased expression of stimulatory G proteins and to the heightened immune and endocrine responsiveness to GnRH. In this report, we document gender differences in expression of Gα<sub>q/11</sub> protein in lymphoid organs in non-autoimmune DBA/2 mice. In an effort to address the mechanisms for the gender differences in G-protein expression, we used competitive reverse transcription PCR to quantitate mRNA for stimulatory G proteins in immune cells under various hormonal conditions. We quantitated the expression of Gα<sub>q/11</sub> mRNA and protein under physiologic hormonal alterations, i.e. throughout the estrous cycle in female mice. We demonstrate that expression of Gα<sub>q/11</sub> mRNA and protein in lymphoid organs is significantly increased on the afternoon of proestrus compared to metestrus. Additional studies demonstrate that exposure to GnRH or to estrogens significantly increases the expression of Gα<sub>q/11</sub> mRNA in immune cells. These findings support an active role for hormonal modulation of G proteins in the gender differences in endocrinologic and immunologic responsiveness to GnRH.