From 1983 to 1988 the densities of beaver colonies in traplines from within two blocks were compared. The first block (RB, 275 km2) was included in a larger area where wolves were reduced almost 60% over three winters. The second block (UB, 265 km2) received no wolf-control treatment. Beaver trapping, formerly prohibited, was allowed in 1984 in 5 of 11 trapline units of RB and 5 of 9 units of UB after the first wolf reduction. The density of colonies (0.8/km2) remained stable in UB, even where beaver trapping was allowed. In RB a 20% increase in colonies occurred after 3 years in units not opened to beaver trapping, but the numbers decreased to their former level 2 years after wolf control was terminated. Where wolf reduction and trapping occurred synchronously, colony numbers remained unchanged, but they decreased by 30% following suspension of wolf control. We do not recommend wolf reduction as a management tool when beaver density is high.