Real-time B-mode ultrasonography was used to study in vivo the behavior of bifurcated aortic grafts (Dacron knitted) implanted over a period of 1 to 88 months previously in 67 patients, 28 of whom (42 per cent) were hypertensive. Most grafts showed an increase in size, when compared with the original one, which appeared to be closely related to arterial pressure (P less than 0.05). This increase was not dependent on the time elapsed from implant.