In Japan, the post-dilution method is preferred to maintain the dialysis efficiency of low molecular weight substances in continuous hemodiafiltration (CHDF). In contrast, the pre-dilution method is preferable to ensure a stable filter lifetime, especially for membranes with cytokine absorptive characteristics that are at high risk of membrane coagulation. However, the impact of the dilution method on the removal performance of adsorptive membranes for cytokines remains unclear. This study aimed to investigate the effect of different dilution methods on the adsorption clearance of cytokine on polymethylmethacrylate (PMMA) membranes by in vitro experiments. Bovine albumin, interleukin (IL)-6, and creatinine were added to phosphate-buffered saline to achieve final concentrations of 3.5 g/dL, 1000 pg/mL, and 10 mg/dL, respectively. The test solution was passed through the 1.8 m