Conflicting results have emerged from studies that have examined nontrophoblastic tumor tissue for the presence of human chorionic gonadotropin (hCG) by immunoperoxidase techniques. We evaluated 11 lung carcinomas, ten breast carcinomas, and ten renal cell carcinomas for the presence of immunoreactive hCG by the avidin-biotin-horseradish peroxidase method. The hCG was found in 36% (4/11) of lung tissues, 10% (1/10) of breast tumors, and none of renal tumors. These values are lower than earlier reports for the frequency of detected hCG in the tumor tissue, but they are similar to several more recent studies. The possible reason for these discrepancies are discussed.