Brain scintigraphy with Tc99-pertechnetate (Tc99-scan) was performed 4 times in 95 consecutive stroke patients: on average 5 days, 18 days, 103 days and 194 days after the stroke. The type (infarct, hematoma), size and localisation of the lesion was evaluated by CT-scan performed 3 times in all: on average 3 days, 18 days and 207 days after the stroke. The detection rate of Tc99-scan was 31% on day 5, 47% on day 18, 18% on day 103 and 9% on day 194. The detection rate was however highly dependent upon: (i) the localisation of the lesion, i.e. superficially localised lesions were nearly always identified (90%) while infarcts localised deep in the hemisphere were identified in only 20% of the patients; (ii) the size of the lesion, i.e. large deep infarcts were seen with a much higher frequency than small deep infarcts. The detection rate of the CT-scan was practically not dependent upon the time of investigation: 63% on day 3, 70% on day 18, 69% on day 207. The detection rate of the Tc99-scan and CT-scan was nearly identical for large superficially localised lesions 2-3 weeks after the stroke. In this period, however, CT-scan identified 30 deep infarcts. Only 12 of these were identified by Tc99-scan.