Alpha-fetoprotein (AFP) is a well-established marker of hepatocellular carcinoma, yolk sac tumor, and other AFP-producing tumors mostly of gastrointestinal origin. The high sensitivity as well as the high specificity of AFP among other cancer markers was established by Abelev et al. (1963) and Tatarinov (1963, 1964), using an immunodiffusion technique by their evolutional discovery of an oncofetal nature of AFP. Following the development of sensitive radioimmunoassay (Ruoslahti and Seppala, 1971; Nishi and Hirai, 1973), the specificity of AFP as a marker of hepatocellular carcinoma was somewhat reduced, since low but frequently increased serum levels of AFP were demonstrated in patients with hepatitis and liver cirrhosis, a known underlying condition of hepatocellular carcinoma. Furthermore, the diagnostic sensitivity of AFP became lower as a result of instituting an ultrasonographic screening system for early detection of hepatocellular carcinomas, although AFP measurement itself is included in this system (Okuda, 1986; Liaw et al., 1986; Regan, 1989). Thus, this is not to deny the value of AFP as a marker of hepatocellular carcinoma. On the other hand, it is now possible to restore or even increase the specificity of AFP by analysis of its sugar chain heterogeneity with lectins (Breborowicz et al., 1981; Miyazaki et al., 1981).