results revealed that l histidine strongly suppressed the dna synthesis of the human normal lung fibroblast cell with pdgf or fcs human kidney mesangial cells were cultured overnight in a culture medium containing 10 vol fetal calf serum fcs subsequently the culture medium was replaced with a 0 1 vol fcs culture medium and it was cultured for 24 hours subsequently l histidine his as a test substance was added in an amount to give a concentration of 10 or 30 mm then further fcs was added to give a final concentration of 5 vol and the mesangial cells were cultured for 24 hours six hours before the completion of the culturing bromodeoxyuridine brdu was added to the culture system after the completion of the culturing the brdu uptake into the cells was assayed by elisa enzyme linked immunosorbent assay as a control only 5 vol fcs was added to the culture medium when the brdu uptake in the control was defined as 100 the value of each of the groups was calculated and the results are shown in fig6 the result show that l histidine strongly suppressed the dna synthesis of the human kidney mesangial cell with fcs in accordance with the present invention an excellent organ fibrosis inhibitor particularly a liver fibrosis inhibitor containing histidine as the active ingredient preferably histidine together with cysteine and or cystine as the active ingredients is provided other than the use in forms of pharmaceutical agents medical products for liver diseases for example chronic hepatitis liver fibrosis cirrhosis and liver cancer the organ fibrosis inhibitor particularly the liver fibrosis inhibitor can be used in various foods.