In a study of over 100 auditory nerve fibers, every fiber exhibited spontaneous spike discharges although the rates ranged between <1/sec to 100/sec. Histograms of the interspike interval of this activity all show a mode at about 4 msec and a tail that decays exponentially. This pattern is consistent with that generated by a Poisson-like process with a dead time. A histogram of the number of fibers encountered vs spontaneous rate shows that certain ranges of rates occur more frequently than others. Distinct peaks occur at <5/sec and 40/sec with less distinct peaks at 60/sec and 70/sec. This distribution of spontaneous activity can be seen in individual cats and is apparently unrelated to either physiological condition or level of anesthetization of the animal. There is no correlation of rate of spontaneous discharge with the frequency of tone to which the unit is most sensitive. However, there is some indication that units with low rates of spontaneous discharge have higher thresholds to acoustic stimuli than units with high spontaneous rates. [This work was supported in part by the U. S. Army, U. S. Air Force Office of Scientific Research, and the U. S. Office of Naval Research; in part by the National Science Foundation (Grant G-16526): in part by the National Institutes of Health (Grant MH-04737-02); and in part by research grant B-1344, National Institute of Neurological Diseases and Blindness, National Institutes of Health, Public Health Service, U. S. Department of Health, Education, and Welfare.]