In order to examine the mechanism by which the oral carbonaceous adsorbent, AST-120 delays the appearance of glomerular sclerosis, experiments were carried out in 120 male Sprague-Dawley rats weighing 285-320 g. The rats were first subjected to 2/3, 3/4, and 4/5 nephrectomy (n = 40). The experiments were begun at 2 weeks after the surgery, and were performed over an 8-week period. Half of each group (n = 20) was administered 1 g/day of liquid AST-120, and the other half received liquid vehicle solution with pair feeding in each group. In the 2/3 nephrectomized group the administration of AST-120 delayed the occurrence of glomerular hypertrophy and prevented the appearance of glomerular sclerosis without any significant differences in renal function, systemic blood pressure (SBP), and urinary protein excretion (U-P). In the 3/4 nephrectomized group the administration of AST-120 delayed the appearance of glomerular hypertrophy and sclerosis with significant decreases in SBP and U-P. In the 4/5 nephrectomized group the administration of AST-120 delayed the appearance of glomerular sclerosis and prevented a decrease in renal function. It is concluded that administration of the oral adsorbent AST-120 delays the occurrence of glomerular sclerosis by delaying the appearance of glomerular hypertrophy, systemic hypertension, and the increase in proteinuria. It can be therefore mentioned that the accumulating substances in the digestive tract worsen the abnormal milieu of chronic renal failure.