Changes in spatial structure of the native riparian mustelid guild including the European mink Mustela lutreola, otter Lutra lutra, polecat M. putorius and stoat M. erminea in connection with the expansion of the American mink M. vison were analysed on the basis of a radiotracking and snowtracking study in the upper reaches of the Lovat river, NE Belarus. Four main questions were investigated: (1) how does habitat selection differ between the native mustelids in the absence of American mink? (2) does habitat use change following the arrival of American mink and, if so, how? (3) does habitat selection differ between the two mink species? (4) how does European mink density before American mink arrival compare with American mink densities after the disappearance of European mink? Before American mink naturalization, European mink density was highest at small rivers and brooks, otter density was highest at larger rivers, polecats were found to inhabit all types of river banks and shores at a similar density. No changes in otter habitat use were found after the American mink expansion. Gradually, during four years of the American mink expansion, European mink became rare at small rivers. However, at brooks used less frequently by American mink there was little change in European mink density. Radiotracking data showed that American mink drive European mink away from rivers. European mink are still found at brooks, however, such small streams arc used more frequently by European mink males than by females, because there is not enough food to rear a litter. Following the American mink expansion, the polecat population along the banks and shores was reduced by approximately half. In riparian habitats American mink seems to be a more competitive species than the polecat and as a result, polecat populations tend to decline there. Furthermore, as with European mink, polecat females are at an even greater competitive disadvantage due to their smaller body size. The most important difference in habitat selection of the native mink and naturalized mink is that the European mink inhabited banks and shores and usually stayed close to aquatic ecosystems, whereas the American mink fairly frequently inhabited marshes, pools and even dry forest.