Singular perturbation methods are used to establish the conditions under which full-order observers can be designed so as to reconstruct the state vectors of multi-variable linear systems containing ‘ parasitic ’ elements, and the resulting design procedure is illustrated by designing a full-order observer for a third-order system. This procedure for the design of full-order observers is the dual of the procedure developed by Porter (1976) for the design of stabilizing state-feedback controllers for multivariable linear systems containing ‘ parasitic ’ elements.