Ten healthy male volunteers received intravenous regional anaesthesia of the upper limb on two separate occasions using 40 ml of 0.5% prilocaine or 40 ml plain 0.5% chloroprocaine by random allocation. Using a double-blind method, the onset and recovery of sensory block was tested (pinprick) in the four main nerve areas. The onset and recovery of motor block was measured by squeezing a rubber balloon connected to a manometer. The symptoms after deflation of the tourniquet were recorded. Seven volunteers in both groups developed total anaesthesia in 20 min. Complete motor block occurred in 12.3 min with prilocaine and 11.3 min with chloroprocaine. Sensation recovered in all areas in 7.6 min with prilocaine and 10.0 min with chloroprocaine (ns). Motor function recovered in 8.4 and 12.0 min respectively (p less than 0.01). Six volunteers in the chloroprocaine group showed signs of venous irritation and/or antecubital urticaria in the test arm for 30-45 min after the deflation. Four volunteers in the chloroprocaine group had increased in heart rate (greater than 20%) and one of them short periods of junctional rhythm during the first 2 min after tourniquet deflation. Mild, short-lived CNS side effects occurred in both groups.