Existing patient data and serum samples from 1677 patients participating in The Netherlands Cooperative Study on the Adequacy of Dialysis-2 (NECOSAD-2) were used in this study. Data was collected at 6-month intervals between April 1997 and September 2002. The study was performed to detect EPO hyporesponsive patients, EPO antibodies and PRCA in dialysis patients. This evidence concerns the gene EPO and pure red-cell aplasia.