Systems identification trials are described for determining the dynamics involved in drug-induced paralysis. The aim is to provide automatic control of levels of muscle relaxation in anaethetised patients undergoing surgery. A linearised model has been successfully identified giving combined pharmacokinetic and pharmacodynamic parameters. The-model has implications for the design of feedback controllers, and simulations involving the use of Smith predictors are presented. Feedforward control is also considered to allow for perturbations in paralysis caused by general anaesthetic drugs used to induce unconsciousness.