Objective To study the role of fibroblasts in the pathomechanisms of renal interstitial fibrosis(RIF). Methods Growth behavior and apoptos, of renal interstitial fibroblasts in cultures, established using renal biopsies of casts with and without RIF, were studied. Results There were significant alterations in the growth behavior, the differentiation pattern of potentially mitotic fibroblast populations and programmed cell death in cultures derived from kidneys with RIF, as compared with cultures of normal origin. Conclusion The abnormal growth and apoptosis of fibroblasts may play an im-portant role in RIF. Inhibiting the proliferation and promoting the programmed death of fibroblasts may be benificial to patients with RIF.