Abstract: The invention disclosed includes a method of and apparatus for reducing the differential pressure holding a section of a drill string by lowering the hydrostatic pressure of the drilling fluid in the well bore adjacent the section being held. This is done by sealing the annulus between a fishing string and the well bore with a packer located above the section being held and lowering the level of drilling mud in the fishing string. In the embodiment described, the drilling mud level is lowered by swabbing drilling mud from the fishing string with a swab that is lowered and raised in the fishing string by a flexible swab line. A seal is provided between the swab line and the upper end of the fishing string to allow drilling mud to be pumped down the fishing string if necessary to for any reason, such as to circulate out a kick. The swab and the packer are provided with valves that can be opened to allow such circulation.