Traps were baited with a variety of foods such as carcasses of small vertebrates, meat scraps, canned dog food, ground horse meat and bacon grease. At each capture, sex, weight, and individual formula of the opossum, based on toe-clipping and ear-clipping (Fitch, 1952), were recorded. Also recorded was the exact site of capture as located in one of 84 divisions of the Reservation and estimated in feet from some named landmark. Notes on breeding condition, pelage, injuries, parasites and general appearance were also taken at the time of capture. For opossums caught in 1951 and 1952, the hind foot measurement was recorded. Often, attempt was made to follow the released opossum to determine the direction and distance of its homeward travel but this was difficult because of brushy terrain and secretive habits of the animal. An opossum being followed would almost invariably take refuge in a tree if it caught sight of the observer. Other information regarding the animal's habits was obtained from tracks in snow or soft soil and from the distribution and contents of scats. Carcasses of opossums which had fallen victim to predators were found on a few occasions and in some instances clues as to the identity of the predator were obtained. One hundred and seventeen opossums were live-trapped and handled a total of 276 times. Six of these were dead when first found in the traps. The remaining 111 were marked and released. In addition, 207 pouch-young carried by adult females were recorded and 115 of these were individually marked by toe-clipping. Some of the opossums that were marked while in the mother's pouch were subsequently recaptured when they were well-grown, independent young, or adults, affording information on growth and dispersal. HABITAT The habitats of the Reservation have been described briefly by Fitch (1952) and by Leonard and Goble (1952). More than half the area consists of steep wooded slopes with mixed second growth forest, consisting of elm, hickory, oak, walnut, ash, honey locust, hackberry and osage orange, in about that order of abundance, with thickets of blackberry, crabapple, wild plum and grape. Fallow fields and pastures of the upland and valley floors alternate with the woodland. The varied habitat provides numerous different food sources. Along the edges of the hilltops there is a nearly continuous limestone outcrop with a lower outcrop paralleling it. These rock ledges, well distributed throughout the area, provide an abundance of den sites and most of the opossums definitely trailed to a home base were found to be utilizing dens in the rock ledges. Two small creeks on the area have some water for most of the year. As compared with wooded bottomland of larger stream courses in Douglas County and those counties adjoining it, the Reservation area probably supports a relatively low population density of opossums. "Sign" has been found in much greater abundance in near-by areas supporting a heavier woodland.