Differences in the potential yearly increase of young among deer (Odocoileus virginianus) in the northern as compared with the southern region of New York State were studied by examining [female] speci- mens collected between Jan. and May during 4 yrs. (1939-42). A larger % of successful breeding and a larger av. number of embryos per doe were indicated for the southern region. In this region the most frequent number of embryos for adult [female] [female] was 2, whereas in the northern region it was 1. Salient ecological features of the 2 regions are discussed. Differences in the essential nutrients available to deer are indicated as an important contributory factor to the disparities observed in breeding potential.