To evaluate the feasibility of using serum iron as a tumor marker for renal cell carcinoma, a retrospective review of serum iron, hemoglobin, hematocrit, mean corpuscular volume and pathology in patients with renal cell carcinoma was carried out. From January 1985 to December 1989, preoperative serum iron was obtained in 82 patients; 27 had stage I, 5 stage II, 23 stage III and 27 had stage IV disease. The serum iron levels (micrograms/dl) were 81.6 +/- 33.2 in stage I, 57.8 +/- 18.9 in stage II, 59.6 +/- 34.6 in stage III and 45.6 +/- 32.7 in stage IV disease, which were significantly lower as compared with the data (114.6 +/- 38.9) of a control group. Postoperative serum iron levels were available in 31 patients following nephrectomy and all showed an increase as compared with preoperative data except 2: 1 with recurrence and the other with progression of disease. It was concluded that the serum iron level may be used as a useful tumor marker in staging and follow-up of renal cell carcinoma.