Acute dialyser reactions in patients treated by haemodialysis are uncommon. We present two cases of such reactions, both in patients using a polysulfone, steam-sterilised dialyser. Patient 1 suffered from recurrent attacks of acute dyspnoea, hypoxia and hypotension that occurred early in dialysis sessions, whereas patient 2 presented with unexplained episodes of severe hypotension and vomiting in the initial phases of dialysis. After switching to a cellulose triacetate dialyser, both patients became asymptomatic during all subsequent dialysis sessions, but intentional (patient 1) and accidental (patient 2) rechallenge with the polysulfone dialyser induced an immediate recurrence of the symptoms. A literature search yielded 30 additional cases that have been reported since the turn of the century. All dialysers that provoked acute reactions contained membranes belonging to the polyarylsulfone family (polysulfone/polyethersulfone, PSu/PESu). Manifestations, usually occurring within the first 30 minutes of dialysis, included dyspnoea (69%), hypotension (66%), hypoxia (44%), bronchospasm (25%), chest pain (22%), pruritus and/or urticaria (22%) and abdominal symptoms (22%). Of the 32 patients, 14 were switched to a different PSu/PESu containing dialyser, which resulted in cross-reactivity in 12 of them (~85%). They could be treated safely with dialysers containing substituted cellulose (n = 8) or polyacrylonitrile (n = 4). Sixteen patients were successfully switched directly to a dialyser containing substituted cellulose (n = 11), polymethylmethacrylate (n = 4) or polyacrylonitrile (n = 1). Two patients were lost to follow-up. As rechallenges may be harmful, patients with acute reactions to PSu/PESu membranes should not be further tested in a trial-and-error fashion with similar membranes, but be switched directly to a non-PSu/PESu dialyser.