In PET studies we have shown the usefulness of cobalt radionuclides for the visualization and quantification of ischaemic damage in stroke. In the present study, we explored 57Co2+ as a SPET tracer. Uptake of radioactivity was estimated by using a cobalt enhancement ratio defined as the ratio of cobalt uptake in the affected region versus a similar volume in the non-affected contralateral side. Clinical status was assessed with the Orgogozo stroke score at the time of scanning and at least 60 days after admission. Nineteen patients (11 men, 8 women) with a middle cerebral artery stroke were examined with 57Co2+ SPET 0-30 days after stroke onset. Our investigations show enhanced cobalt uptake in the infarcted brain tissue in patients with a major stroke and little clinical improvement. There was a significant correlation between the cobalt enhancement ratio and the Orgogozo score at the time of scanning and discharge. Our results suggest that 57Co2+ SPET is suitable for determining the extent of (possibly calcium-mediated) damage in stroke and in the assessment of potential therapeutic interventions.