We studied the influence of different modes of hemodialysis (HD) on plasma levels of β2-microglobulin (P-β2-m) and its correlation to changes in leukocyte count, complement activation (C3a), and elastase generation. The influence of dialyzer membrane, membrane surface area, duration of treatment, and blood flow was analyzed with respect to post-HD levels of P-β2-m. Twenty patients underwent 12 modes of bicarbonate hemodialysis in random order (n = 252) using three different membranes (Cuprophan [CU], hemophan [HE], or polyamide [PA], two dialyzer areas, and fast (400 mL/min) or slow (200 mL/min) blood flow (Qb) for 2 or 4 hours, respectively. All dialysate was collected and β2m was analyzed (D-β2-m). After correction for hemoconcentration, P-,β2-m concentrations were found to have decreased significantly during treatment with all three membranes (CU, 0.9 ± 0.3 mg/L, P = 0.002; HE, 1.2 ± 0.3 mg/L, P < 0.001; and PA, 8.3 ± 0.3 mg/L, P < 0.001). Elimination of P-β2-m was influenced by type of membrane (P < 0.001) and ultrafiltration volume (P = 0.0019) but not by membrane area or Qb. The largest reduction in P-β2-m(-10.4 mg/L) was achieved by the following treatment combination: PA membrane, large dialyzer area, and low Qb for 4 hours. P-β2-m decreased more during PA dialysis at low Qb for 4 hours (-9.9 ± 0.5 mg/L) than during high Qb for 2 hours (-6.8 ± 0.5 mg/L, P < 0.001). D-β2-m was significantly higher after PA dialysis than after CU or HE dialyses (P < 0.001) and was influenced during PA dialyses by pre-HD P-β2-m (r = 0.57, P < 0.001). Changes in P-β2-m correlated to bioincompatibility markers, such as leukopenia (r = 0.20, P = 0.0014), Ma activation (r = 0.31, P < 0.001), and elastase production (r = 0.17, P = 0.012), but the statistical significance was due to covariation. This study shows that membrane type and ultrafiltration volume all have influence on β2-m removal and that dialysis time seems to be more important than membrane area and Qb. No factual correlation was seen between changes in β2-m and markers of bioincompatibility.