The method of interferon therapy has not been clarified in hemodialysis patients with renal cell carcinoma. Two hemodialysis patients with renal cell carcinoma were treated with natural interferon-alpha. The serum levels of interferon-alpha in both patients were measured after 24, 48, 72 and 96 h of injection. In case 1, the serum concentration of interferon-alpha after 24 h of injection at a dose of 3 x 10(6) reached a maximum and decreased gradually. In case 2, the serum concentration of interferon-alpha reached a maximum 24 h after injection at a dose of 3 x 10(6) and decreasing gradually after this. After an injection of interferon-alpha at a concentration of 6 x 10(6) 7 days later, the serum concentration of interferon-alpha reached a maximum 48 h after the injection and decreased gradually thereafter. The serum interferon-alpha concentrations of these cases were higher than normal renal function patients in other literature. It is necessary to modify the interval between injections for hemodialysis patients with renal cell carcinoma.