The water balance in the upper layers of permafrost, near Mayo, Yukon Territory, has been monitored at two sites by neutron probe and heave displacement tubes. Results obtained between 4 April 1984 and 2 May 1985 are reported. The principal forces controlling water movement are temperature-induced: net water movement depends on the thermal regime and temperature-dependent variations in the hydraulic conductivity (k//f) of the frozen soil. Moisture incorporation into frozen ground from the thawing active layer continues throughout the period from snowmelt to late fall freeze-back. A result of this is that the permafrost layer just below the active layer is enriched annually with water derived from the atmosphere.