The researches of tumor markers started at the discovery of Bence Jones protein in 1848. Now, alpha-fetoprotein and carcinoembryonic antigen are popular tumor markers and recently several tumor markers using the methods of monoclonal antibodies have been invented. Usually we measure the tumor markers in sera, so the early diagnosis of cancer by the tumor markers are sometimes difficult. For the early diagnosis by tumor markers, inventions of new tumor markers, improvement of assay systems and materials and the combination assays of several tumor markers have been tried. The researches of tumor markers are progressing with those of cancer. We hope we will be able to diagnose early cancer or precancerous state by tumor markers.