beta 2-microglobulin (beta 2M) is a small molecular mass protein associated with dialysis amyloidosis. We have studied beta 2M elimination in end-stage renal disease (ESRD) patients treated by peritoneal dialysis. In 12 patients on continuous ambulatory peritoneal dialysis (CAPD) and 7 patients on intermittent peritoneal dialysis (IPD) 30.4 +/- 4.2 mg/day and 21.3 +/- 1.8 mg/12 hour of beta 2M, respectively, were removed by dialysis fluid. Approximately the same amount of beta 2M was removed by each of four 2-L exchanges in CAPD; however, the most efficient removal of beta 2M was in the first IPD exchange. Serum beta 2M levels in these patients were 25.7 +/- 4.4 and 31.4 +/- 5.2 mg/L, respectively. In 24 patients on hemodialysis using cuprophan membrane the serum level of beta 2M was 55.1 +/- 4.1 mg/L. After a 3-month dialysis on polyacrylonitrile (PAN) membrane, the serum beta 2M level decreased to 45.0 +/- 2.3 mg/L. A substantial amount of beta 2M was removed by urine, 14.6 +/- 2.3 mg/L, and saliva, 2.3 +/- 0.4 mg/L. This study has shown markedly increased beta 2M levels in patients on conventional hemodialysis treatment, predisposing to beta 2M-related amyloidosis. A significant amount of beta 2M was removed during both CAPD and IPD treatment.