To assess the effects of hydrosalpinx fluid on human cytotrophoblast viability and function in vitro. Human cytotrophoblasts obtained from third-trimester placentas were cultured in vitro with hydrosalpinx fluid, and cell viability and protein production were assayed. A university hospital. Ten hydrosalpinx fluid samples obtained from seven women with clearly diagnosed hydrosalpinges. Recovery of hydrosalpinx fluid by transvaginal aspiration or at the time of surgery. Cell viability was assessed by the XTT assay. Secretion of trophoblast oncofetal fibronectin (tropho-uteronectin) and beta-hCG by cultured trophoblasts was determined by Western blot and ELISA of the culture media. With increasing concentrations of hydrosalpinx fluid from 0% to 20%, there was a significant increase in trophoblast cell viability (1.63-fold increase in 20% hydrosalpinx fluid). Likewise, both Western blot and ELISA assays demonstrated a significant increase in tropho-uteronectin production by trophoblasts with increasing hydrosalpinx fluid concentrations (3.76-fold increase in 20% hydrosalpinx fluid). beta-Human chorionic gonadotropin production also increased significantly in the presence of hydrosalpinx fluid (3.31-fold increase in 20% hydrosalpinx fluid). These findings suggest that hydrosalpinx fluid improves human trophoblast viability in vitro and enhances the production of tropho-uteronectin and beta-hCG by these cells.