The distribution of otters (Lutra lutra) in Europe is largely fragmented, mainly due to historic anthropogenic causes. Nevertheless, in eastern Germany a large coherent area is inhabited by a viable otter population. In this paper, the mitochondrial genome of 81 otters is studied by RFLP analysis of PCR-amplified 1.5 and 2.5 kb long fragments, particularly to estimate the amount of genetic variability of European otters, and to identify possible geographical population subsets for conservation management. No restriction site polymorphism was detected within the control region (1.5 kb), but polymorphism of cleaving sites in the 2.5 kb fragment could be assigned to three haplotypes. Two occurred exclusively in a comparatively small area northwest and west of Berlin, which may be considered a region of increased genetic variability in otters. The low level of mtDNA variability in European otters might be due to genetic drift in postglacial founder populations with long-term low densities, and continuous historical overhunting. (C) 1999 Elsevier Science Ltd. All rights reserved.