The present studies analysed the uterine free secretory component (SC) response to steroid hormones, and correlated effects on SC with those on IgA. Administration of oestradiol for 3 days to ovariectomized rats significantly increased the levels of SC in uterine secretions, when compared to those in saline-injected controls. This response was dose-dependent and specific for oestrogens, since progesterone, testosterone and glucocorticoids had no effect. The oestradiol-induced elevation in SC levels occurred in parallel with that of IgA. Time course studies of SC and IgA in uterine secretions indicated that both proteins accumulated in nearly identical patterns following oestradiol administration. The oestradiol-stimulated accumulation of SC, however, appears to be independent of IgA since dexamethasone treatment with oestradiol decreased IgA but not SC levels in uterine secretions. In contrast to dexamethasone, progesterone antagonized the oestradiol effect on both uterine IgA and SC. The uterine SC response to oestradiol was also observed in vitro. Incubation of uterine tissue following oestradiol exposure in vivo resulted in a significant accumulation of SC in the culture medium, when compared to levels from control uteri. Addition of either cycloheximide or colchicine to uterine incubation media significantly decreased the effect of oestradiol on SC accumulation. These results suggest that oestrogen regulation of uterine SC may involve stimulation of its synthesis. In addition, our findings indicate that oestradiol control of SC in uterine secretions may be responsible for the movement of IgA from uterine tissues to lumen.