The authors examined the serum of 164 hemodialysed chronic uremic patients for the detection of anti-N-like antibodies in two time intervals (in 1982 and 1988). The hemodialysis treatment was done in both intervals with regenerated, formaline-sterilized capillary dialysers. In 1982 antibodies could be detected in 5 out of 44 patients (11.3%) while in 1988 the ratio was 3 out of 120 (2.5%). The control group consisted of 40 healthy blood donors and 27 such dialysed patients who were treated only with new, ethylene oxide-sterilized single use capillary dialysers. The special cold agglutinine was not detectable in the serum of the subjects of the control group.