The antitumor activities of a 70 kDa highly glycosylated fragment (OVMα70F) in the α-subunit separated from pronase-treated hen egg white ovomucin were examined in a double grafted tumor system. BALB/c mice received simultaneous inoculations of Meth-A tumor cells in the right flank (1×106 cells) and left flank (2×105 cells). Solutions (250 μl) of OVMα70F (1000 μg/mouse/day) or physiological saline (PS) were injected into the right tumor on days 3, 4, and 5, and the mice were raised for 21 days. OVMα70F induced direct and almost complete inhibition of growth of the right (treated) tumor and acted indirectly and moderately on growth of the left (distant), compared with each control tumor. The microscopic observations of tumor tissues on day 21 showed that a greater portion of the OVMα70F-treated right tumor cells was necrotic, whereas a smaller portion of the left one was degenerative. In the tumor tissues of OVMα70F-treated mice neutrophils, macrophages and lymphocytes were found to have massively accumulated and the angiogenesis (the formation of new capillary blood vessels) was inhibited.