1. Blood leptin levels are increased in obese subjects and seem to play a major role in the hypothalamic regulation of appetite and energy expenditure. 2. We measured plasma leptin levels in a cohort of 46 patients on maintenance haemodialysis treatment and 26 control subjects. 3. Higher body mass indices were associated with higher plasma leptin levels in both groups. 4. The increase was more pronounced in the dialysis group than in the control group ( P = 0.001), leading to inappropriately high plasma levels. 5. Haemodialysis with low flux cellulosic dialysers did not result in a decrease in plasma levels, while dialysis with high flux dialysers and haemodiafiltration led to a substantial reduction of the initial value to 76.95 ± 14.89% ( P = 0.013) and 62.90 ± 24.94% ( P = 0.001) respectively. 6. Our data suggest that high flux dialysis membranes can decrease plasma leptin levels and that inappropriately high plasma leptin levels may play a role in the nutrition of haemodialysis patients.