To measure the changes in fluid volume flow rates through an artificial fracture undergoing slip, silicone oil was pumped through a sawcut in welded tuff in the radial flow geometry during rotary shear. The flow rates at constant normal stress and constant fluid pressure gradient were measured at different amounts of fracture slip. The fluid volume flow rate for a smooth fracture increases at first then decreases with ongoing slip. For a rougher fracture the flow rate decreases over the whole range of slip. The results have implications for fluid withdrawal from reservoirs and underground waste disposal. ¿ American Geophysical Union 1992