The morphological and functional characteristics of isolated subcutaneous resistance vessels (about 230 microns internal diameter) from 13 patients treated for essential hypertension for a median period of 14 months and from 15 matched normotensive controls were examined. The blood pressure of the patients and the controls were not significantly different at the time of examination. However, although compared with the controls, the lumen diameter of the vessels from the patients was not significantly different, the media thickness to lumen diameter ratio was 19% greater. Furthermore, although there was no difference in the active pressure response of the vessels from the two groups, the vessels from the patients had a lower sensitivity to calcium, relaxed faster after a contraction and the sensitivity to exogenous noradrenaline shifted more to the left with cocaine. Since the abnormalities found here have previously also been found in vessels from patients with untreated essential hypertension, the study suggests that despite antihypertensive treatment to normotensive levels for about 1 year, some morphological as well as functional characteristics of the resistance arteries are not fully normalized. This could have consequences for the prognosis of essential hypertension.