This study investigated the properties of propofol when given by subanaesthetic infusion to provide sedation as an adjunct to spinal anaesthesia for lower limb surgery in 40 patients. Sedation, defined as sleep with preservation of eyelash reflex and purposeful reaction to verbal or mild physical stimulation, was satisfactorily achieved and maintained with minimal complications. The mean duration of infusion was 98 minutes and a mean infusion rate of 3.0 mg/kg/hour was required in patients over 65. This was significantly less (p less than 0.005) than the 4.1 mg/kg/hour required in younger patients. Recovery was impressively rapid; patients regained full consciousness approximately 4 minutes after the end of infusion, and were free from minor postoperative sequelae. Conversion to general anaesthesia was achieved in three patients where surgery encroached outside the analgesic field of the regional block, simply by increasing the infusion rate to approximately 10 mg/kg/hour.