Summary Red‐cell indices, including the diameter/thickness ratio (D/T) derived from mean cell diameter (MCD) and mean cell volume (MCV), were determined in a study of 203 medical out‐patients. A close correlation was found between D/T and MCH and between D/T and MCHC.

Red cell indices were determined in two groups of patients with chronic obstructive airways disease, a total of 60 patients. Bone marrow aspiration for the assessment of iron stores was also carried out in the majority of these patients. Values below the accepted lower limit of normal for mean corpuscular haemoglobin concentration (MCHC) and mean corpuscular haemoglobin (MCH), and values above the accepted upper limit of normal for the diameter/thickness ratio (D/T), suggested the possibility of iron deficiency in 20 %, 23 % and 33 % of these patients respectively. 14 (26 %) of the 54 patients whose bone marrows were examined were found to have no stainable iron stores in the marrow fragments and were therefore considered to be definitely iron deficient. There was a probably significant relationship between the absence of iron stores and an increased D/T ratio, a reduced MCH, but not a reduced MCHC. The results of a dietary study suggested a possible relationship between the presence of iron deficiency based on the examination of bone marrow iron stores and a low iron intake. It is concluded that iron deficiency, which may be a common occurrence in chronic obstructive airways disease, is at least a contributory factor in the production of abnormal red cell indices in such patients.