OBJECTIVE: To examine the effectiveness of imatinib mesylate in the treatment of nephrogenic systemic fibrosis (NSF). METHODS: Two patients with stage 5 chronic kidney disease and NSF were treated with oral imatinib mesylate at a dosage of 400 mg/day. Skin thickening and tethering were assessed using the modified Rodnan skin thickness score (MRSS), and knee joint flexion contractures were measured with a goniometer. RESULTS: Each patient displayed progressive reduction of skin thickening and tethering, with a steady decrease in the MRSS, following the initiation of imatinib mesylate treatment. The patient who had knee joint contractures achieved increased knee extension with passive range-of-motion exercises once his skin thickening and tethering had begun to decrease. Within weeks of stopping imatinib mesylate, the skin changes recurred in each patient. Recurrent skin thickening and tethering again improved in the patient who resumed taking imatinib mesylate for longer than 2 weeks. Skin biopsies performed both before and after initial dosing of that patient revealed less fibrosis and less staining for type I procollagen after imatinib mesylate treatment, but essentially unchanged tissue gadolinium content. CONCLUSION: Imatinib mesylate treatment decreases fibrosis and results in the relatively rapid and steady improvement of skin changes and knee joint contractures in patients with stage 5 chronic kidney disease and NSF, despite the persistence of gadolinium in the tissues. Because skin changes recurred after discontinuation of imatinib mesylate, the duration for which treatment may be required is undetermined.