The concentrations of pyridinoline (Pyr), a novel marker of bone resorption, were simultaneously measured in both serum and urine samples by ion-paired high-performance liquid chromatography in 27 patients with predialysis chronic renal failure. The patients consisted of 19 males and 8 females, whose creatinine clearance (Ccr) ranged from 2.5 to 47.6 ml/min. The influence of residual renal function on serum Pyr and the clinical significance of serum and urinary Pyr were analyzed in patients with predialysis chronic renal failure. There were significant correlations between serum Pyr and serum Cr (r = 0.76) and between Pyr clearance and Ccr (r = 0.70). In addition, significant correlations were observed serum and urinary Pyr (r = 0.64) and between both serum and urinary Pyr and HS-PTH (r = 0.96 and r = 0.61, respectively) and osteocalcin (r = 0.80 and r = 0.73, respectively). However, serum bone alkaline phosphatase isoenzyme (ALP3) was correlated with neither serum nor urinary Pyr. There was no correlation between the ratio of serum Pyr/serum Cr and the metabolic bone markers (HS-PTH, osteocalcin and ALP3). There was a correlation between Ccr and urinary Pyr, although it was statistically significant (p < 0.1). These date led to the following conclusions: (1) serum Pyr in patients with oredialysis chronic renal failure is influenced by reduced renal function and (2) urinary pyr shows a state of bone resorption when an adegvafe level of renal function is maintained. This suggests that patients with an advanced stage of renal osteodystrophy are included among cases of predialysis chronic renal failure.