One hundred sera samples, obtained during the early postoperative period from 11 patients after a partial hepatectomy, were assayed for alpha-fetoprotein (AFP). None were AFP-positive by radioimmunoassay, despite clinical and biochemical recovery associated with normal liver regeneration. AFP was elevated in 29% of patients with acute hepatitis, 34% of patients with chronic active hepatitis, and in 75% of patients with massive hepatic necrosis. The mechanism and significance of AFP elevations in some patients with acute and chronic hepatitis is uncertain but probably does not reflect normal liver regeneration.