Changes in the demography and habitat use of three small rodent species (Clethrionomys gapperi, Microtus pennsylvanicus and Peromyscus maniculatus) and snowshoe hares (Lepus americanus) were monitored from July to November 1978. Bi-weekly live-trapping programs in six natural habitat types and in two naturally revegetating areas provided detailed demographic information on small rodent populations. A similar bi-weekly live trapping program in four natural habitat types provided detailed demographic information on snowshoe hares. A snap-trap census program provided information on habitat use and reproduction of small rodents in a wider geographic range of habitats than that sampled by the live-trapping areas. Preliminary analyses presented in this interim report suggest that: 1. C. gapperi is most common in mature forested areas (specifically areas with white spruce, balsam fir, birch, balsam poplar or aspen tree cover). 2. M. pennsylvanicus most commonly inhabits area with little or no tree cover – both live-trapping and snap-trapping indices indicated that M. pennsylvanicus preferred successional areas or grass dominated areas (e.g., willow scrub, grass meadows, marshes, edges of waterbodies). Tamarack-black spruce bog was also heavily used. 3. P. maniculatus was most abundant in balsam poplar, aspen and succession areas but generally showed few preferences for any particular habitat (areas dominated by birches were more heavily used than expected). 4. L. americanus was most numerous in black spruce forest in the summer and fall followed by balsam poplar, aspen and jack pine forests. In the early spring, however, balsam poplar habitat was most utilized. 5. Data on other species of small mammals (red squirrels, flying squirrels, chipmunks, various species of small rodents and shrews) were insufficient for determination of habitat preferences or an analysis of population changes. Continued research in each study area, particularly in the early spring period, is required.