Objective To study the expression of basic fibroblast growth factor(bFGF)in the kidney tissues of chronic interstitial nephritis(CIN).Methods Expression of bFGF was assayed in 30 patients with CIN and 5 normal persons by SP method of immunohistochemical technique.The average gray value and average optical density of the bFGF positive parts and its ratio with the whole visual field had been measured with video analysis system.Results The expression of bFGF in the kidney tissues of CIN was significantly stronger than that in normal tissues.The average gray value,average optical density and the positive areas were significantly high compared with that of normal cases.Conclusion The bFGF can promote the proliferation of fibroblasts and monocytes in renal interstitial patients and lead to renal interstitial fibrosis in the end.