The long-term survival of oligodendrocytes in the absence of axons in adult animals was studied following Wallerian degeneration of the optic nerves of adult rats for periods up to 22 months. In contrast to the findings in development and in young animals, large numbers of oligodendrocytes survived during this time period even when deprived of axonal stimuli. The morphological phenotype of many of these cells differed from those of normal oligodendrocytes, and their oligodendrocytic nature was confirmed at a light microscopic level using antibodies to carbonic anhydrase, and at an electron microscopic level by using antibodies to myelin oligodendrocyte glycoprotein. Although there did appear to be some loss of oligodendrocytes over time, a large proportion appeared to remain intact. Many of the remaining cells and processes appeared to resemble resting or quiescent cells. The survival of these cells demonstrates the differential susceptibility of mature and developing oligodendrocytes to loss of axonal stimulus and also indicates a possible reserve capacity for repair following central nervous system injury.