The relationship of serum ferritin and transferrin levels to risk of cancer was examined in a population of 21,513 Chinese male government workers in Taiwan who have been followed prospectively since 1975. On the basis of a previous study in the Solomon Islands, increased ferritin and decreased transferrin levels were predicted for those men who developed cancer. The results were consistent with the prediction. The mean serum ferritin was higher at the start of the study in 192 men who had died of cancer or who had developed primary hepatocellular carcinoma (PHC) as of July 1983, as compared to their controls. The mean serum transferrin level was lower in men who had died of cancers other than PHC. The estimate of relative risk of cancer death for a man with 200 ng ferritin/ml and 200 mg transferrin/dl, as compared to a man with levels of 20 ng/ml and 400 mg/dl, respectively, is 2.9. These serum iron-binding protein levels are at the extremes of the "normal" range. Men who subsequently died of cancer had lower hemoglobin, lower hematocrit, lower albumin, and higher globulin levels at the start of the study than did the controls. These results are consistent with the hypothesis that increased iron stores increase the risk of cancer. However, direct assessment of iron stores prior to disease was not possible, and the same constellation of findings may be consistent with other explanations.