There is a paucity of data on muscle biopsies in females of mixed ages in terms of age-related changes. Cross sections of autopsy material including the quadriceps femoris and biceps brachii muscles were obtained from 23 healthy women, aged 24-82 years, who had suffered sudden death. We calculated the percentage of the number, and the mean diameter, of type I and type II muscle fibers within the fascicles as well as in their peripheral parts. The number of type II fibers were shown to reduce significantly with age ( < 0.005), especially in the fascicle periphery, but the percentage of type 1 fibers did not alter significantly. It was noted that type II fibers diminished in size with age, indicating a relationship between fiber size and age. This result became more apparent in the fascicle periphery ( < 0.05). In women, type II muscle fibers were seen to reduce in size and number with advancing age. We postulate that regular physical activity can increase the size of type II muscle fibers, thus helping to both prevent and treat age-related muscle loss.