In this paper the problem of pole-assignment in linear time invariant multi-variable systems is generalized to include the case of systems incorporating integral control action. In some control system design poroblems, integral feedback is introduced in conjunction with proportional one in order to ele-minate steady-state errors arising from sustained disturbances. Most published work deals with the introduction of integral as well as pro-portional feedback of some or all of the state variables of the system under control. This paper establishes a new design procedure of proportional plus-integral controllers (PI-controllers) based on the feedback of system output variables. The controllability of the compensated system is investigated and a necessary and sufficient condition for the augmented system to be controllable is deri-ved. The existance problem of such type of modal-controllers is discussed and a necessary condition for complete pole-assignment of the closed-loop system is derived. A pratical design algroithm of this type of controllers is developed, and it is used to design a PI-controller for a VSTOL aircraft.