Hyperparathyroidism is usually listed among the possible reasons for impaired response to recombinant human erythropoietin (rHuEPO) in patients with renal disease. However, its relevance in the context of other causes of renal anaemia, and the mechanisms by which it may worsen anaemia, are not entirely clear. Possible pathogenic links between anaemia and parathyroid hormone (PTH) include reduced erythropoiesis due to calcitrol deficiency, and direct or indirect effects of PTH on erythropoietin release, red blood cell (RBC) production, survival, and loss. Studies of these mechanisms have produced disparate results, possibly because secondary hyperparathyroidism may have only a relatively minor role in anaemia that may be masked by the confounding effects of other factors with greater impact. Variations in medical treatment or study methodology may also have affected study results. Severe parathyroid overfunction may contribute to the severity of anaemia in uraemic patients and diminish rHuEPO responsiveness in a minority of patients. However, overall, the importance of hyperparathyroidism appears to be minor compared with other factors such as iron deficiency or inflammation.