Hemolysates from 100,000 people who visited the Kyushu University Hospital and affiliated hospitals during the past 15 years were screened for hemoglobinopathies using electrophoresis on thin-layer starch gel; those exhibiting an abnormality were characterized further on clinical, biochemical, and genetic grounds. Of about 97,000 adult and 3,140 cord blood samples, 29 contained electrophoretically detectable abnormalities in the heterozygous condition. Another 17 samples had quantitative changes in the levels of the minor hemoglobin components. Of the thalassemic conditions, 12 involved beta-thalassemia, 3 alpha-thalassemia, 1 delta beta-thalassemia, and 1 delta-thalassemia. Among 45 carriers of beta-thalassemia from 12 families, 5 were noted to have thalassemia intermedia since they exhibited much more severe hemolytic syndromes than those with typical beta-thalassemia minor. The frequency with which we could detect a structural variant of Hb A in the adults by electrophoresis was one in 3,800 samples. About one in 8,000 carried a beta-thalassemia gene.