Previous studies have shown that Kampo (traditional Chinese) prescriptions, mainly Wen-Pi-Tang (Onpi-to, [symbol see: text]), have a useful effect in patients with chronic renal failure (CRF). We aimed to examine the long-term effect of Kampo prescriptions on serum creatinine (Cr) among patients with CRF. Patients with serum Cr levels of 2 mg/dl more were enrolled if they had at least 4 recordings of serum Cr in the previous 6 months or more, and were followed-up until the start of dialysis. Eight patients aged 24-59 years with serum Cr 4.5 mg/dl were enrolled in the study for 40 to 402 weeks (mean; 228.1 +/- 118.8 weeks). The cause of CRF was chronic glomerulonephritis in 7 patients and systemic lupus erythematosus in 1 patient. The end points of the study were the slope of the reciprocal of the serum Cr concentration plot against time using Mitch's method, and the predicted period of pre-dialysis. The predicted pre-dialysis period was defined as an increase in serum Cr by 10 mg/dl. As a result, the individual slopes were improved in 6 of 8 cases, in particular, in 4 of 5 Wen-Pi Tang-treated cases. The average slope was improved significantly (p < 0.01) in Wen-Pi-Tang-treated cases, although it showed only a tendency to improve in all 8 cases. The predicted pre-dialysis period was prolonged from 79.2 +/- 74.8 weeks to 389.5 +/- 355.4 weeks and 55.6 +/- 37.0 weeks to 262.4 +/- 145.8 weeks in all 8 cases and Wen-Pi-Tang-treated cases, respectively. The observed pre-dialysis period was 228.1 +/- 118.8 weeks, which showed that Kampo prescriptions prolonged the predicted period for 186 additional weeks. In conclusion, this study demonstrated that the Kampo prescriptions, consisting mainly of Wen-Pi-Tang, retarded the progression of CRF.