Psychomotor retardation is important in some depressed patients. We found that speech pause time (SPT) during a counting test correlated with the reaction time of both depressed patients and controls. It also correlated with global psychomotor retardation measured on Widlocher's scale. We demonstrated increased SPT in unipolar depressives, and also in retarded depressives as a group when compared with controls and with non-retarded depressives. SPT varied diurnally in controls, but not in depressed subjects. It did not correlate with biological markers of depression (REM sleep latency and the dexamethasone suppression test). It did, however, shorten during clinical improvement with antidepressant chemotherapy.