One hundred seventy-five patients with features of ectopic pregnancy were studied, of whom 95 were subsequently shown to have an ectopic pregnancy. Paired blood and urine samples were assayed for human chorionic gonadotropin (hCG) by two radioimmunoassays, one immunoradiometric assay for intact hCG and an immunoradiometric assay for free beta subunit that also detects the “beta core” of hCG in urine. Qualitative testing was also performed using the Tandem Icon method of immunoconcentration on a membrane. The quantitative results for intact hCG showed an approximately unitary relationship between concentrations in both fluids, with a close correlation (r=0.84, gradient=1.01). The qualitative tests for hCG in both serum and urine were positive in all patients with ectopic pregnancy. The Tandem Icon is equally useful in blood and urine, whereas quantitative assays are more reliable in the blood. Quantitation of urinary hCG is not recommended because of the variable dilution of the glycoprotein in this fluid.