Bone marrow haemosiderin iron was correlated with various laboratory parameters of iron status in order to define a reliable laboratory index of marrow iron stores. Marrow iron, serum iron, plasma transferrin, transferrin saturation, iron absorption, red cell iron incorporation and serum ferritin were measured in 21 non-dialysed, 20 peritoneal dialysed and 34 haemodialysed patients with chronic uraemia. Diagnostic accuracy of the laboratory tests in terms of diagnosing reduced marrow iron stores was expressed as the predictive value of a positive test and a negative test, and efficiency. Diagnostic efficiency of serum iron, plasma transferrin and transferrin saturation was too low to be of value in the individual patient. Iron absorption and red cell incorporation had a higher diagnostic efficiency, but are unpractical for routine use. Serum ferritin displayed a high diagnostic efficiency and appears to be a reliable index of marrow iron stores, suitable for sequential monitoring of iron status in uraemic subjects.