Thymectomy at 3 days of age (Tx-3) in B6A female mice results in an autoimmune oophoritis that has only been successfully overcome by the transplant of an intact thymus or an injection of T cells. In Tx-3 mice levels of thymosin alpha 1 (TSN alpha 1), a potent thymic hormone involved in the development of helper T cells, was previously shown to be high after 7 days. By 60 days levels of TSN alpha 1 returned to levels found in intact mice. By this age ovarian dysgenesis was also complete and accompanied by high circulating levels of auto-oocyte antibody (AOA), estradiol-17 beta (E2) and testosterone (T). In the present study injections of antisera to TSN alpha 1 were given to Tx-3 mice in an attempt to decrease circulating TSN alpha 1 levels. We reasoned that this treatment should inhibit lymphocyte differentiation, and possibly in turn aid in overcoming the ovarian dysgenesis. After treatment of the Tx-3 mice, dysgenic ovaries persisted and high levels of AOA remained similar to the untreated Tx-3 mice. Levels of E2 and T, however, were returned to those found in intact mice. These results suggest that there is a sensitive balance between the thymus and the ovary that may not be related to changes in only a single thymic hormone.