Endometriosis is a common gynecological disorder of unclear pathogenesis. We have established an in vitro model to investigate phenotypic similarities and differences between normal endometrial and endometriosis cells. Highly purified cultures of epithelial and stromal cells were isolated from normal endometrium and endometriosis implants. Morphological features as well as immunocytochemical markers confirm these isolates as epithelial and stromal cells. Potential hormone responsiveness was established by the documentation of estrogen receptor mRNA in epithelial and stromal cells isolated from both tissue types. Expression of this receptor protein was verified in stromal cells by competitive radioligand binding, revealing comparable receptor numbers and dissociation constants. CA-125 is selectively secreted in similar concentrations by epithelial cells isolated from both tissue types. PRL secretion is selectively exhibited by progestin-stimulated stromal cells from both tissue types. Our findings demonstrate that highly purified epithelial and stromal cells cultured from normal endometrial and endometriosis tissues express the same phenotypic and functional markers as their in vivo counterparts. These cultures provide useful models to identify endometriosis-specific cell products that contribute to the pathogenesis of this disorder.