To identify possible clinically valuable markers of metastatic renal cell carcinoma, we measured the serum concentrations of several commercially available biomarkers in 117 patients with this disease. The alpha-fetoprotein level was measured in 75 patients and was elevated in 8 (11%); elevation did not correlate with the presence of liver metastasis. Beta subunit of human chorionic gonadotropin levels increased in 8 of 83 patients tested (10%). C-terminal parathyroid hormone levels were measured in 79 patients and were elevated in 15 (19%); their serum creatinine level was normal. Thirteen of this group had normal serum calcium levels, whereas 7 patients with hypercalcemia and no clinically evident bone metastasis had normal parathyroid hormone levels. In only 2 of 72 patients, serum lactate dehydrogenase and its isoenzyme 1 were elevated. Only 1 of 85 patients had mildly elevated serum carcinoembryonic antigen, in contrast to 3 of 7 patients with metastatic transitional cell carcinoma of the renal pelvis who had moderately elevated carcinoembryonic antigen. Elevations in alpha-fetoprotein, human chorionic gonadotropin, and parathyroid hormone correlated with the course of the disease in 13 patients for whom follow-up measurements were available; measurement of these markers, however, is only useful in a small proportion of patients with metastatic renal cell carcinoma.