In this study, we investigated a possible association between the degree of macrophage activation - as measured by serum neopterin concentrations - and disturbances of iron metabolism, determined by the concentrations of ferritin and serum iron, in patients with malignant disorders. Additionally we evaluated correlations between these factors and the degree and type of anaemia. Seventy-three patients, who suffered from non-Hodgkin's lymphoma (NHL) (n = 43), Hodgkin's disease (n = 11), myeloma or monoclonal gammopathy of unknown significance (n = 9), myelodysplastic syndrome (n = 1), and solid tumours (n = 9), were examined. Mean neopterin levels were raised in all groups, patients with NHL showing the highest concentrations. Ferritin but not neopterin concentrations were higher in males than in females. A significant correlation was found between neopterin and ferritin concentrations (p less than 0.01). Considering only female patients the strength of the correlation was the same (p less than 0.02). In addition, we found inverse correlations of neopterin with haemoglobin and iron concentrations (all p less than 0.01). Similar relationships existed in patients during follow-up. Our results support the hypothesis of an association between the degree of activation of macrophages and the development of anaemia by a shift or iron towards the storage sites.