Using light microscospy, cross sections of the superior vestibular nerve were compared in 2 tree-dwelling species of squirrels (Sciurus carolinensis and S. niger) and 3 ground-dwelling species (Spermophilus tridecemlineatus, S. mexicanus, and S. variegatus). Fiber number, internal minor diameter of the axon, and axon area were measured for 31,959 fibers taken from 5 males of each species. Significant differences were not found within or among species, suggesting that climbing behaviors are not correlated with these morphologic features of the superior vestibular nerve.