It was hypothesized that pentoxifylline might improve the response to recombinant human erythropoietin (rh-Epo) in anemic renal failure patients. Sixteen patients with ESRD and rh-Epo-resistant anemia, defined by a hemoglobin of <10.7 g/dl for 6 mo before treatment and a rh-Epo dose of > or =12,000 IU/wk, were recruited. They were treated with oral pentoxifylline 400 mg o.d. for 4 mo. Ex vivo T cell generation of tumor necrosis factor alpha (TNF-alpha) and interferon gamma (IFN-gamma) from the patients was assessed before treatment and 6 to 8 wk after therapy. A total of 12 of 16 patients completed the study. Before therapy, the 12 patients' mean hemoglobin concentration was 9.5 +/- 0.9 g/dl. After 4 mo of pentoxifylline treatment, the mean hemoglobin concentration increased to 11.7 +/- 1.0 g/dl (P = 0.0001). Baseline ex vivo T cell expression of TNF-alpha decreased from 58% +/- 11% to 31% +/- 23% (P = 0.0007) after therapy. Likewise, IFN-gamma expression decreased from 31% +/- 10% to 13% +/- 10% (P = 0.0002). Pentoxifylline therapy may significantly improve the hemoglobin response in patients with previously rh-Epo-resistant anemia in renal failure. This may occur due to inhibition of proinflammatory cytokine production, which could interfere with the effectiveness of rh-Epo.