In an immunohistochemical study of the presence of the beta subunit of human chorionic gonadotrophin (hCG) in ovarian neoplasms it was found that hCG was detectable in 42% of ovarian epithelial tumors, an incidence of hCG synthesis which very closely approximates that found in radioimmunoassay studies. There was no relationship between the capacity of an ovarian neoplasm to synthesize hCG and the histologic type of the tumor, the degree of malignancy of the neoplasm, or the prognosis.