The entry of [125I]-labelled low density lipoprotein (LDL) into different regions of the aortic intima has been studied over a 6 hour period in both normotensive and renal hypertensive rabbits fed a normal diet. Studies have also been carried out in previously hypertensive rabbits in which the blood pressure was normalized with parenteral hydralazine during the six hour period, in which entry was studied. In the normotensive rabbits entry into the aortic intima was less than 1 mug of LDL protein/100 mg dry defatted weight over the 6 hour period with greatest entry into aortic arch intima and significantly less into both the thoracic and abdominal aortic intimae. Hypertension increased the entry into the arch and into aortic arch intimae. Hypertension increased the entry into the arch and into the thoracic and abdominal segments but this was only statistically significant for the aortic arch. The entry of [125I] LDL into the intima in those rabbits in which the hypertension had been normalized was similar to that for the hypertensive rabbits. The results suggest that hypertension in the normal fed rabbit increases lipoprotein entry into the arterial wall by an effect on vessel wall permeability rather than by a direct effect of filtration pressure.