To evaluate the Springfusor infusion device for clinical use in an Intensive Care Unit and to compare the technique of intermittent bolus and constant infusion of muscle relaxants, we undertook a prospective double-blind randomized placebo-controlled study. Twenty critically ill ventilated patients requiring muscle paralysis were investigated. Although we could show no clinical advantage in infusing vecuronium, the Springfusor provided a more constant level of paralysis compared with hourly bolus doses. The device is robust, easy to use and reduces nursing workload. This may translate into cost-saving improvement in patient care if the Springfusor is used to provide muscle relaxation, sedation and analgesia.