Regional cerebral blood flow was studied in 17 bipolar I depressed patients (DSM-IV criteria) with single photon emission computed tomography (SPECT). Visual analysis of images revealed no abnormality in eight patients and abnormal findings in nine patients. In the nine patients with abnormal findings, all showed regional decreases of the uptake of (99m)Tc-D,L-hexamethylpropylene amine oxime (HMPAO, four in the frontal region, two in the basal ganglia, and three in both the frontal region and the basal ganglia). The patients with visible SPECT abnormalities had significantly higher scores on the Hamilton Rating Scale for Depression (HDRS).