(Uploaded by Plazi for the Bat Literature Project) A method was devised for estimating aspect ratio, wing ratiOj wing area, wing loading, and wing length from study skins of bats. These measures were taken of 136 species representing 15 families. Wing area and loading are positively, and wing length negatively, correlated with size. Aspect and tip ratios are independent of size and of each other. Distinctive combinations of some of these variables characterize groups of bats that presumably have similar flight modes. Speed is positively correlated with aspect ratio and tip index, but regresses significantly only on the former. Long tips coupled with low aspect ratio may characterize hoverers. Long wings and short tips may characterize bats that are capable of remaining airborne at slow speeds. Most bats with low aspect ratios are forest dwellers, whereas species with high aspect ratios are migrants and foragers in open areas.