Transgenic mouse which produces human alpha-fetoprotein (AFP) ubiquitously was used to study carbohydrate structures of AFP produced by various tissues as well as that in the serum. A series of tissues from the transgenic mouse were cultured in vitro and the AFP produced was analyzed by affinity electrophoreses with 4 kinds of lectins. Variable electrophoretic profiles of them suggested that the fine structures of the carbohydrate of human AFPs expressed in the mouse tissues were different. The characterization of human AFP produced by mouse hepatoma which developed in offspring between the AFP transgenic mouse and hepatoma-developing transgenic mouse indicated that the hepatoma AFP was distinct from the liver AFP and that the malignancy-specific phenotypic alteration was common to human and mouse.