Structural changes of capillaries were reexamined in the rat soleus muscle 12 weeks after limb immobilization. Most capillaries were of the continuous type, while capillaries with fenestrations were often observed around degenerated muscle fibers. In some of these fenestrated capillaries, the endothelial cell was partially disrupted and formed a small pore at its fenestrated portion. These findings suggest that the occurrence of capillaries with both diaphragmed fenestrae and pores represent degenerative changes in the long-term immobilized muscle.