We investigated the treatment of renal osteodystrophy (ROD) in Japan and problems concerning the K/DOQI Guidelines. The subjects were 3698 hemodialysis patients (2328 males and 1370 females) with a mean age of 61.4 years. On average, they had been on hemodialysis for 8.34 years. The serum phosphorus level was <3.5 mg/dL in 5% of the subjects, 3.5-5.5 mg/dL in 49%, 5.6-7.0 mg/dL in 33%, and >7.0 mg/dL in 13%. The serum calcium level was <8.4 mg/dL in 16% of the subjects, 8.4-9.5 mg/dL in 47%, 9.5-10.2 mg/dL in 22%, and >10.2 mg/dL in 15%. The intact PTH level was <150 pg/mL in 57%, 150-300 pg/mL in 27%, and >300 pg/mL in 16% of the patients. The first problem is that correcting Ca is not always performed in clinical fields. The uncorrected calcium level was 9.14+/-0.92 mg/dL, while the corrected calcium level [Ca = Ca + 0.8 x (4-Alb)] was 9.26+/-0.93 mg/dL (P < 0.05). The second problem is that the timing of blood collection is not described in the K/DOQI Guidelines. Subjects with a serum phosphorus level >7.0 mg/dL at 3 days after the previous dialysis were selected for assessment. In these patients, the midweek serum phosphorus level (7.13+/-0.15 mg/dL) at was significantly lower than that (8.11+/-0.15 mg/dL) at the beginning of the next week (P < 0.001). These results suggest that it is necessary to specify the timing of measurement and the method of Ca correction when guidelines for management of ROD are established in the future.