The estrogenic activity of benzophenone and its metabolites, benzhydrol and p-hydroxybenzophenone, were investigated in vitro by estrogen receptor (ER) competitive ligand binding assay and in vivo by uterotrophic assay in juvenile female Sprague-Dawley (SD) rats. p-Hydroxybenzophenone as well as diethylstilbestrol and bisphenol A, known xeno-estrogenic compounds, competed with fluorescein-labeled 17 beta-estradiol to bind human recombinant ER alpha in a concentration-dependent manner. Fifty percent inhibitory values (IC50) of diethylstilbestrol, bisphenol A, and p-hydroxybenzophenone were approximately 10(-8), 10(-5), and 5 x 10(-5) M, respectively. However, neither the parent compound nor benzhydrol at concentrations from 10(-9) to 5 x 10(-4) M impaired the binding of 17 beta-estradiol to ER alpha. Juvenile female rats (21-days-old) were given s.c. injections of benzophenone, its metabolites, and 17 beta-estradiol for 3 days. Administration of p-hydroxybenzophenone (100-400 mg/kg) elicited an increase in absolute and relative uterine weights in a dose-dependent manner and 17 beta-estradiol (10 micrograms/kg) increased uterine weight approximately fourfold relative to control. The uterine response caused by both compounds was accompanied by an increase in luminal epithelial height and stromal cells in the uterus and an increase in thickness of vaginal epithelial cell layers with cornification. In contrast, benzophenone and benzhydrol at a dose of 400 mg/kg affected neither uterine weight nor histological changes of the uterus and vagina. These results indicate that p-hydroxybenzophenone, a metabolite of benzophenone, exhibits intrinsic xeno-estrogenic activity in the female reproductive tract.