A lifting hook for lifting open-frame steel joists comprises a casing having a shaft passing through it. The shaft has a lifting eye at one end and a hook member at the other end. The hook member comprises a U-shaped body having a transverse width selected to be less than the gap between the angles that form the upper flange of the open-frame joist. The hook member has a throat that is larger than the width of the flange. The shaft is spring-loaded so that the hook member is pulled toward the lower bearing surface of the casing so that once the hook member has been inserted into the joist, it is keyed to the flange and will not come loose.