Ictal and interictal SPECT measurements using 99mTc-HMPAO are helpful in localising an epileptic focus. 24 patients (12 women and 12 men; mean age 30 years) suffering from temporal lobe epilepsies with unilateral EEG foci were examined. In all patients a presurgical evaluation including sphenoidal and foramen oval electrodes was carried out. The analysis of SPECT measurement was done visually and semi-quantitatively, comparing the data with findings in healthy persons (10 women and 10 men; mean age 24 years). The etiology of the epilepsy was confirmed by histological investigation in 16 cases, and by CT and MRI in 8 cases. The findings were gliosis in 6 cases, astrocytoma in 3 cases, cysts in 4 cases, and angioma in 3 cases. In 8 cases no pathological findings could be detected. In 46% of cases interictal SPECTs exhibited a focal hypoperfusion corresponding with the EEG-focus. In ictal SPECTs this could be found in 75% of cases. In all 10 patients without morphological findings or with gliosis (proved by histological investigations) a hyperperfusion coincident with the EEG-focus appeared in ictal SPECTs.