The relationship between essential hypertension and abnormalities of the proximal resistance vessels (small arteries) is reviewed, with particular emphasis on their structure. 2. There seems to be good evidence that the media: lumen ratio of these vessels is increased, and this may account for the increased pressor response. 3. Whether there is also growth is not clear, and it is possible that the altered structure is due to redistribution of existing cells. 4. Regardless of the basis for the altered structure, it appears that in essential hypertension the altered vascular structure is in itself sufficient to explain the increased peripheral resistance. 5. Paradoxically, the altered vascular structure does not seem to be the main determinant of blood pressure, but the altered vascular structure appears to allow it to perform its function in the most convenient fashion. 6. It is suggested that the interest in vascular structure lies in connection with therapy, for correction of blood pressure without correction of vascular structure will probably not prevent all the consequences of the disease. 7. Current therapies do not appear to be able, in the short-term, to normalize vascular structure, indicating that there is a need to find other more specific ways of correcting vascular structure.
