By means of Datura stramonium agglutinin (DSA) affinity electrophoresis, human alpha-fetoprotein (AFP) was resolved into five bands, AFP-D1, D2, D3, D4 and D5, in order of decreasing mobility. AFP-D1, which had no affinity for DSA, comprised more than 84% of the intensity of total AFP bands. The percentage of AFP-D2 increased marginally in hepatitis and liver cirrhosis with or without hepatocellular carcinoma. AFP-D3 increased characteristically in hepatocellular carcinoma and AFP-D4, which had the highest affinity for DSA, increased up to 12% in other tumors, mostly of gastrointestinal origin. AFP-D5 showed no consistent changes among the benign and malignant diseases. The assay of AFP-D3 and D4 proved useful as a highly specific marker of hepatocellular carcinoma and other tumors, respectively.