A sensitive procedure involving lectin affinity electrophoresis of alpha-fetoprotein (AFP) was established. AFPs electrophoresed on lectin-containing gels were blotted on nitrocellulose membrane which was precoated with the specific antibody to AFP and stained with peroxidase-labeled anti-AFP antibody. This method could detect as little as 4 micrograms/l of purified AFP dissolved in buffer, or 50 micrograms/l in serum specimens. A number of patients with liver disease have been followed for long periods in Nihon University Hospital, Tokyo. Serum specimens were collected serially and stored frozen. We have reinvestigated retrospectively 6 series of serum specimens by the lectin-immunoblotting technique and found 3 cases that revealed a hepatocellular carcinoma-specific AFP variant at a very early stage, in advance of any other evidence of hepatocellular carcinoma by clinical examination.