Abstract From previous published data on replacement of deep water in Byfjord (Linde, 1970) and obvious relation is found to exist between northerly winds along the west coast of Norway during summer and the volume of deep water being replaced. Northerly summer winds induce upwelling of denser water to shallower depths, which then can spill over the sill and intrude into the fjord basin. The magnitude of replacement appears to be independent of variations in freshwater discharge and climate. Recent observations of current and water properties reveal that the exchange flow across the sill is basicly two-layered: a landward flow in the lower and a seaward flow in the upper layer, with the level of no-net motion located at mid-depth. Short period (2-7 days) variations in the long-shore wind component are well reflected in the exchange flow. Wind speed extremes are followed one to two days later by corresponding extremes in the exchange flow, indicating the approximate response time for the upwelling process. In periods of sustained northerly winds along the coast the inflow attains a saturation speed of about 30 cm/s, which is slightly less than the critical speed obtained from the mean stratification by assuming an ideal two-layer flow across the sill.