The hepatic iron regulator hormone hepcidin consists, in its mature form, of 25 amino acids, but two other isoforms, hepcidin-20 and hepcidin-22, have been reported, whose biological meaning remains poorly understood. We evaluated hepcidin isoforms in sera from 57 control and 54 chronic haemodialysis patients using a quantitative proteomic approach based on SELDI-TOF-MS. Patients had elevated serum levels of both hepcidin-25 and hepcidin-20 as compared to controls (geometric means: 7.52 versus 4.69 nM, and 4.06 versus 1.76 nM, resp., P < .05 for both). The clearance effects of a single dialysis session by different dialysis techniques and membranes were also investigated, showing an average reduction by 51.3% +/- 29.2% for hepcidin-25 and 34.2% +/- 28.4% for hepcidin-20 but only minor differences among the different dialysis modalities. Measurement of hepcidin isoforms through MS-based techniques can be a useful tool for better understanding of their biological role in hemodialysis patients and other clinical conditions.