A qualitative and quantitative study was made of the contacts between muscle cells in the media of the thoracic aorta of hypertensive and normotensive Sprague-Dawley rats. In ultrathin sections, the type and number of contacts per 100 microns cell perimeter and per 100 cell profiles were determined using an image analysis computer. The intercellular contacts in both groups were in the form of simple appositions, interdigitations, intermediate junctions and nexus junctions. In the hypertensive group, there was a reduction in the number of simple appositions and intermediate junctions, but the nexus junctions (which provide intercellular communication) were increased in density. Interdigitations demonstrated no change. Decreased intercellular cohesion may play an important role in the mechanisms by which hypertension predisposes degeneration of the media with progression to ectasia, aneurysm formation and dissection.