Time-domain limitations due to right half-plane zeros and poles in linear multivariable control systems are studied. Lower bounds on the interaction are derived. They show not only how the location of zeros and poles are critical in multivariable systems, but also how the zero and pole directions in uence the performance. The results are illustrated on the quadruple-tank process, which is a new multivariable laboratory process. ? 2002 Elsevier Science Ltd. All rights reserved.