In order to investigate the effects on behaviour of hypertension, age, and the types of antihypertensive agents, we have conducted a retrospective analysis in 100 hypertensive patients receiving chronic treatment in our Hypertension Clinic. A group of 80 normotensive subjects, matched for age, were included in the study. Half of the hypertensive patients were under the age of 50 (young group) and half were over the age of 50 yrs (old group). The antihypertensive agents had not been administered according to any specific protocol, but represented the choice of the individual clinicians treating the patients in the clinic. All patients had received treatment for at least one year, and usually for two years. The behavioural tests performed were designed to measure sensory-perceptive ability, cognitive ability and psychomotor function and were those employed and described in our previous studies. The results achieved were varied, but indicated that older age was associated with an impairment in performance as was blood pressure. Test performances in the young hypertensives were similar to those achieved by older normotensives. These results were more prominent in cognitive and psychomotor functions than in the sensory-perceptive tests. The antihypertensive drugs used also affected these results; the worst behavioural performances tended to be in patients receiving the central nervous system agonists (methyl-dopa and clonidine) and better performances in patients receiving beta-blockers alone when compared with the other groups. Surprisingly, patients receiving diuretics showed poorer performance levels, but these were better in patients who received a beta-blocker in combination with their diuretic.(ABSTRACT TRUNCATED AT 250 WORDS)