Human chorionic gonadotropin levels in concentrated 24-hour urine and serum were determined by a specific radioimmunoassay of beta-human chorionic gonadotropin in 47 patients with genitourinary carcinoma. Elevated human chorionic gonadotropin levels in urine were observed in 6 of 8 patients with active testicular tumor, 3 of 14 with prostatic cancer, 2 of 10 with bladder cancer, 1 of 2 with ureteral or renal pelvic tumors and 2 of 6 with renal cancer. Of the 14 patients with positive urinary human chorionic gonadotropin 4 had undetectable human chorionic gonadotropin levels in the serum. The tumors of all 8 patients with nontesticular cancer who had increased urinary human chorionic gonadotropin levels were in an advanced clinical stage or of poor histological differentiation. Our results suggest that some nontrophoblastic carcinomas of the genitourinary system are capable of ectopic production of human chorionic gonadotropin, particularly if the malignancy is advanced or poorly differentiated. The radioimmunoassay of beta-human chorionic gonadotropin in concentrated 24-hour urine specimens enhances the sensitivity of detection of ectopic human chorionic gonadotropin production.