The verbal learning and fluency of patients with unipolar and bipolar depression were compared to those of normal controls and patients with Huntington's disease. The data demonstrated that the recall and recognition performance of both groups of depressed patients were impaired relative to the performance of normal control subjects. The bipolar patients, however, were more impaired than the unipolar patients on both tasks (P less than 0.024 and P less than 0.022, respectively). In addition, the unipolar patients generated more correct responses on a test of verbal fluency (P less than 0.04). The performance of the bipolar patients was, in fact, similar to that of patients with Huntington's disease, a progressive degenerative disorder that primarily affects subcortical areas.