Abstract: Improved apparatus for isolating a production tubing string in an oil well from the control head whereby pressures higher than the pressure of the control head may be applied through the production tubing string to the producing formation. The apparatus utilizes an outer housing with a telescoping inner mandrel and seals therebetween, with the outer housing being adapted for connection to the control head and the inner mandrel being capable of moving into the control head to make a fluid-tight sealed connection with the production tubing thereby isolating the control head from the higher pressure being applied through the tubing into the formation.