We have been studying about antitum or potency of lignins in foods. Lignins are contained not only in woods but also in edible parts of some fruits and vegetables; such as in stone cells of pears, bamboo shoots, radishes, gourd fruits and nerves of leaves. These lignins are also so stable against cooking that they come into diets. Lignins are IR-spectrophotometrically classified into two species; one belongs to that of latifoliate trees and the other to that of needle-leaf trees. As the models for investigating the antitumor mechanisms of lignins in foodstuffs, we used lignin preparations which were by-produced by some pulping procedures of latifoliate and needle-leaf trees. Lignin preparations produced by sulfite-pulping process were effective to ascitic sarcoma 180. Fifty to 60% of mice to which these lignin preparations had been injected intraperitoneally survived even after the perishment of all the tumor-bearing mice of control. Then, antitumor potency of calcium lignosulfonates from latifoliate trees (L-LS) and needle-leaf trees (N-LS) against the sarcoma was investigated. Many mice treated with these lignosulfonates survived more than 60 days after tumor transplantation (in case of L-LS, 7/10; N-LS, 5/10), though all of the tumor-bearing mice of control run were dead within 25 days. Among these survived animals, no accumulation of ascitic fluid was detected, they appeard to recover from the sarcoma. Alkaline oxidation or demethoxylation of the lignins caused the decrease in the potency. Circumstantial evidences have shown that the configurations of lignin molecules largely take parts in their antitumor ability