The main aim of the study was to establish the degree of disturbance of the cognitive functions typical of the elderly depressed patients. The analysis was based on the results of a 4-week, double-blind, placebo-controlled therapeutic study in which the effects and tolerance of the antidepressant nomifensine were tested in a randomized group of 100 patients. Half the patients were depressed and half nondepressed (a priori stratification, HAM-D 2 18). Tests of central nervous arousal, attention, perceptual grouping, short-term and long-term memory, and complex reaction time were performed. The findings were analyzed as follows: First, baseline differences in cognitive performance, correlative of the stratification into depressed and nondepressed patients, were examined. Second, changes reflecting normalization of cognitive function resulting from the antidepressant treatment were analyzed. For antidepressant treatment, nomifensine, a noradrenaline and dopaminereuptake inhibitor, was used. Results showed that cognitive impairment in primary depression was fairly generalized over different cognitive functions. A global factor of cognitive impairment and a general cognitive improvement factor was found. Both factors are closely connected with the severity as well as the improvement in cardinal symptoms of depression. This relationship was interpreted as due to alterations in central nervous arousal.