This study was designed to examine the effects of oral adsorbent AST-120 on the progression of CRF in patients on strict LPD. Thirteen patients with CRF (serum creatinine: 1.8-8.2 mg/dl) that had been kept on LPD (0.4-0.7 g/kg/day) were enrolled in this study. After LPD alone for 5-24 months, AST-120 (3-6 g/day) was administered concurrently with the LPD for an additional 5-13 months. In 9 of the 13 patients, the slopes of reciprocal creatinine (Cr) vs. time plot linearly declined before AST-120 treatment. After treatment, the slopes of these patients lessened from -0.01 +/- 0.001 to -0.003 +/- 0.001 dl/mg/month (p < 0.01). Because reciprocal Cr did not decline linearly with time before AST-120 treatment in the remaining 4 patients, the slopes of reciprocal Cr could not be compared before and after treatment with AST-120. Seven of the 9 patients had sufficient creatinine clearance (Ccr) data after treatment with AST-120. The decline of Ccr decreased from -0.59 +/- 0.13 to -0.12 +/- 0.12 ml/min/month in these patients. This study has clearly demonstrated that AST-120 compounds the effects of well-controlled LPD on retarding the progression of CRF. AST-120 may remove some uremic metabolite(s) which promote the progression of CRF.