40 young Sprague-Dawley rats in groups of 10 were subjected to treatment with dipyridamole for 1, 2, 4 and 8 weeks. Another 40 sham-treated rats served as controls. The medial portion of the quadriceps femoris muscle was evaluated for total capillarization, fiber area and fiber type composition. Capillary/fiber ratio and mean number of capillaries in contact with each fiber were significantly increased in the rats treated with dipyridamole for 2 weeks and longer. The capillary density, however, did not increase until after 4 weeks of dipyridamole treatment. The fiber area increased gradually with age and was significantly enlarged by dipyridamole treatment after 2 and 4 weeks. All fibers in the examined muscles were of the low oxidative (white) type and no change was recorded in this respect after dipyridamole treatment.