We compared a group of nine patients with panic disorder (DSM-III-R) and depression with a matched control group of nine dysthymic patients without a previous or actual history of panic attacks or anxiety with iomazenil SPECT (single photon emission computed tomography) to evaluate panic-related abnormalities of the benzodiazepine receptor complex. The panic group had a significant decrease (p < .05, U-tests) in the regional activity index (RAI) in the following regions after 2 h: lateral inferior temporal lobes, right and left, medial inferior temporal lobes, left, inferior frontal lobes, right and left. All other regions investigated were not significantly different. The findings may be due to either regional blood flow differences or benzodiazepine receptor effects. The hypothesis that the effects are due to altered blood flow is confirmed to some extent by similar findings in the scans acquired after 10 min. Only the hypoactivity in the left lateral temporal region seemed to be independent of reduced blood flow in panic disorders.