It is known that a decrease in sciatic nerve motor-nerve conduction velocity is occured in rat with experimental hypermyoinositolemia. We found raised blood myo-inositol lvels in uremic patients. It suggests that blood myo-inositol is one of uremic toxins. However, the relationship between the blood myo-inositol levels and reral function was not known. In this study, we have measured the serum free myo-inositol levels in healthy donors, uremic patients under chronic hemodialysrs and renal transplants using a 200 cm column of 5% Ucon on Gaschromatography. Average of serum free myo-inositol levels in 12 healthy donors was 0.46±0.03 mg/dl (mean±S.E). Those of pre- and post- dialysis levels of 21 uremic patints under chronic hemodialysis were 11.19 ± 0.72 mg/dl and 3.77 ± 0.33 mg/dl respectively. The level of serun free myo-inositol was remarkably drawn by hemodialysis. We found that a change of serum free myo-inositol levels in postoperative course of some renall transplants showed just like parallel change of serum creatinine levels of them. Furthermore, the serum free myo-inositol levels were more linealy related to the serum creatinine levels than to the serum urea nitrogen. On the other hand, it seems that the recognition of the relation in high or low serum free myoinositol levels may show some new concepts of unknown diseases excepting renal dysfunction from these results. In some renal transplants, we measured the urine free myo-inositol and serum free myo-inositol, too. We found that there were some relations between the myo-inositol levels and the acute rejections. We observed in four acute rejections of three renall transplants that the urine free myo-inositol contents and the myo-inositol clearance were elevated in a few days prior to the acute rejections. It seems that the measurement of the urine free myo-inositol in post-operative renal transplants is a new methode of predictable and rapid diagnosis of the acute rejection.