In 32 noncirrhotic patients on peritoneal dialysis, mean serum beta 2-microglobulin (s beta 2M) was 26.58 +/- 12.32 mg/l (9.7-63.5). We found a significant correlation between s beta 2M and serum creatinine (sCr; r = 0.760), blood urea nitrogen (BUN; r = 0.573), total creatinine and BUN clearance (r = 0.623 and 0.599, respectively), 24-hour Kt/V (r = 0.638), glomerular filtration rate (r = 0.623), 24-hour urine output (r = 0.669), serum total protein (r = 0.584) (p < 0.01 for all the above r values); beta 2M peritoneal clearance and mass transfer (r = 0.414 and 0.427, respectively; p < 0.05). Our data demonstrate and confirm the contribution of residual renal function in determining s beta 2M levels and it is seemingly more important than beta 2M peritoneal clearance.