Thirty-three in-patients attended for non-contrast enhanced computed tomography (CT) of chest and/or abdomen within a six-week period (11 M, 21 F) . All had measurement of their full blood profile within the previous 72 hours. Patients with a blood dyscrasia or known history of active bleeding were excluded. All patients were imaged using a Siemens Somatom Plus S scanner. The scanning parameters were standardised at 210 mA, 120 kV, 10 mm slice thickness, pitch of 1. Following image review, circular regions of interest (ROI) were defined within the lumina of the aorta and inferior vena cava (IVC) at the level of the superior mesenteric artery origin. The mean attenuation value was calculated using on-board computer software, and recorded. The mean patient age was 59.6 years (range 18-85 years). A non-parametric correlation analysis was performed and a linear regression plot obtained. A significant correlation was demonstrated between haemoglobin measurement and the aortic and IVC attenuation value. The correlation was stronger (r = 0.64) for the aortic attenuation value than for the IVC attenuation values (r = 0.57). In addition, if anaemia is defined as less than 14g/I for a male and less than 12g/I for a female, then, in our study group, no male with an aortic attenuation value greater than 50HU and no female with an aortic attenuation greater than 45 HU was found to be anaemic. The results demonstrate a significant correlation between patients' haemoglobin measurement and the derived aortic attenuation value. We do not propose this as a method of accurately measuring the patient's haemoglobin; however, we feel that it may be possible for a radiologist at non-contrast enhanced CT examination to note the probable presence of anaemia.