Background: Serum β<sub>2</sub>-microglobulin (β<sub>2</sub>M) levels are important in dialysis-related amyloid deposition but can be influenced by dialysis technique. Methods: We measured β<sub>2</sub>M levels in 3 centres using different dialysis regimes. Centre 1 (73 patients) used high-flux biocompatible, centre 2 (72 patients) low-flux biocompatible and centre 3 (142 patients) cuprophane dialysers. Results: β<sub>2</sub>M levels were lower with high-flux biocompatible than with low-flux biocompatible or cuprophane dialysis (22.3 ± 5.4 vs. 43.4 ±13.7 and 37.6 ±13.1 mg/l, respectively; p < 0.001). Levels were higher with low-flux biocompatible than with cuprophane dialysis (p < 0.001), but not if patients dialysed over 10 years were excluded. With low-flux biocompatible (47.4 ± 9.8 vs. 38.7 ± 15.2 mg/l; p < 0.01) and cuprophane dialysis (43.4 ± 8.2 vs. 36.7 ± 13.0 mg/l; p < 0.02), β<sub>2</sub>M levels were higher in patients dialysed over 5 years than in those dialysed less. Despite β<sub>2</sub>M levels increasing as residual renal function declined, there was no similar rise with high-flux biocompatible dialysis. Conclusions: Techniques allowing significant convection maintain lower β<sub>2</sub>M levels over many years. Membrane flux, not biocompatibility, is the main determinant of β<sub>2</sub>M levels in routine practice.