A new invertibility criterion for linear time-invariant multivariable systems is derived. This criterion is stated as a rank condition of a matrix whose elements consist of the system parameters ( <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">A,B,C,D</tex> ) instead of the Markov parameters ( <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">D,CB, ..., CA^{n-1}B</tex> ).