Substituted 8,9-diphenyl-6,7-dihydro-5H-benzocycloheptenes 6-8, which are ring-fused analogues of (Z)-trans-4-hydroxytamoxifen, (E)-cis-tamoxifen, and (E)-cis-4-hydroxytamoxifen, were synthesized from 7-methoxy-1-benzosuberone. The hydroxy compounds 6 and 8 were individually prepared via a common synthetic intermediate from which either the perfluoro-p-tolyl or the methyl ether functions could be cleaved specifically. Compounds were assayed for binding affinity to estrogen receptors in cytosol and in MCF-7 whole cells and for growth inhibition of MCF-7 cells in vitro and rat uteri in vivo. The endocrinological properties of the cyclic analogues 5-7 paralleled those of the corresponding derivatives of tamoxifen although in the MCF-7 assay 6 was slightly less effective than 4-hydroxytamoxifen at 10(-6) and 10(-7) M. The compound 8 analogues to cis-4-hydroxytamoxifen antagonized the growth stimulation by estradiol of MCF-7 cell or rat uterus growth, and it is therefore an antiestrogen, but its potency was somewhat less, both as an antiestrogen and an estrogen, than reported for cis-4-hydroxytamoxifen attributable to modification of the biochemical properties of the latter by isomerization to the more potent trans isomer. Curiously, in the absence of estradiol, compound 8 stimulated MCF-7 cell growth at low concentration (10(-8) M) but inhibited growth at higher concentration. In contrast, compound 7, which lacked the hydroxy function, was a full estrogen in the rat uterine growth assay. These compounds should be ideal for further structure-activity studies of triarylethylene-based antiestrogens without complications caused by isomerization.