Observers are often used to provide estimates of inaccessible states which can be used for the purpose of pole placement. The design of the composite-observer feedback scheme may be separated into the design for the original system assuming the states to be accessible and the design of the observer. At times it is desirable that the poles of a system are attracted towards preferred regions of the complex plane rather than be placed at exact locations. To achieve this one may use multivariable root locus techniques and it is shown here that observers could be used to make estimates of inaccessible states available for the purposes of zero placement and manipulation of root-locus asymptotic directions. Irrespective of whether one uses a full- or reduced-order observer it is shown that as for the case of pole placement the overall root locus design may be separated into the design of the original system assuming that all the states are accessible and the design of the observer.