The effect of the in vivo administration of various triphenylethylene antioestrogens and physiological (0.05 microgram) versus pharmacological (0.5--5 microgram) doses of oestradiol-17 beta (Oe2) on the uterotrophic process in general and the nuclear accumulation and cytoplasmic depletion and replenishment of uterine oestrogen receptor was determined. Regardless of the dose of Oe2 the changes in uterine wet weight, total protein and incorporation of [3H]thymidine into DNA and [14C]leucine into protein were the same at 24 h. The anti-oestrogen receptor was also studied. The net increase, above control, of cytoplasmic oestrogen receptor at 24 h and 48 h after Oe2 injection was approximately 0.35 and 0.77 pmoles/uterus, respectively. The effect of anti-oestrogens (U-11,100A, CI628, en- and zuclomiphene) on the increase in cytoplasmic oestrogen receptor at 24 h and 48 h measured from maximally depleted levels was nearly identical to the Oe2 induced net increase. This suggests that in both cases these particular increases represent newly synthesized receptor and that Oe2 causes some receptor replenishment through a recycling process.