Using the theory of analytic functions the stability of linear multivariable systems defined by a set of delayed differential equations is considered. It is shown that such systems may be described by transfer function matrices which determine their stability. The theory of coprime factorization of transfer functions is used to extend some of the concepts of algebraic system theory to the delayed case. These results are then used to develop a Nyquist type criterion for the analysis of feedback stability under proportional and dynamic feedback. The theoretical development is illustrated by an example of a two state system with three unstable poles.