Abstract: Biological pacemaker systems direct temporal regulation in most animals.  Circadian timing increases an organisms chance of survival by preparing it in advance for its daily routine.  Stereotaxic lesioning of the mammalian circadian pacemaker, the suprachiasmatic nuclei (SCN), creates clockless, arrhythmic animals.  Laboratory studies have shown that SCN-lesioned animals such as rats and hamsters live normal life spans in a sheltered environment.  Fitness studies are lacking, however, for wild, free-living animals that have been deprived of their neural biological timing systems.  As part of a research project being conducted on the adaptiveness of circadian rhythmicity, this study will: 1.  test reproductive success of SCN-lesioned female chipmunks, 2.  observe den activity of control and SCN-lesioned chipmunks, and 3.  contrast mortality of chipmunks for the Main Project on the campus of Mountain Lake Biological Station, VA and a remote, auxiliary tract within the Mt. Lake wilderness.  To test reproductive success, eight artificial concrete/PVC pipe burrow systems were constructed and installed in an area of high chipmunk density.  After initial baiting, den occupation was checked by visual observation and opening of the den.  To record natural burrow activity, an automated data logging system recorded movements of one control and one SCN-lesioned chipmunk on the Main Project Area.  Loss of radio contact indicated a departure from the den.  Den activity was downloaded onto a PC computer and displayed as a daily actogram of radio contact.  As a handling control project, all resident chipmunks within the auxiliary tract were trapped, identified, and marked to distinguish individuals.  Fifteen were chosen for SCN-lesioning and 15 for controls.  After repatriation, survival and well-being were monitored for the remainder of the summer by visual observation and live-trapping methods.  Chipmunks visited the artificial burrows, but none took up residence during the initial eight week period.  More time is necessary to examine reproductive success.  Daily actograms for two animals indicate that both control and SCN-lesioned chipmunks remained diurnal in their activity patterns.  Comparison of mortality in the two study areas must await future data.  However, SCN-lesioned animals do survive and prosper at least several weeks after repatriation.