In the present studies, we observed the regulation of water channel gene (AQP-CHIP) expression by estradiol (E2) and anordiol, an antiestrogen with agonist activity, in immature female rat uterus. Antisense and sense oligonucleotide primers corresponding to the consensus sequences of two rats AQP-CHIP water channels were synthesized and used to amplify a cDNA fragment that was reverse-transcripted from rat uterine total RNA preparation. E2 administered as a single dose of 40 micrograms.kg-1 to immature female rats induced a significant increase in AQP-CHIP mRNA expression 9 h after treatment. The lowest effective doses of E2 and anordiol were 40 and 50 micrograms.kg-1, respectively. The stimulatory effect of anordiol was more pronounced than that of E2. The present results suggest that AQP-CHIP water channel gene expression may be involved in E2- and anordiol-mediated water imbibition and luminal fluid production in the uterus.