The effect of clonidine, an alpha 2 agonist, on sensory and motor blockade during spinal anesthesia was studied in 44 ASA physical status I II patients scheduled for orthopedic surgery. The patients were randomly allocated into three groups given 15 mg of 0.5% hyperbaric tetracaine (HT), within group I (N = 14) 1 ml isotonic saline, in group II (N = 15) 0.5 ml saline solution and 0.5 ml clonidine (75 micrograms), and in group III (N = 15) 1 ml clonidine (150 micrograms). Sensory blockade (SB) was evaluated by pinprick and motor blockade (MB) according to Bromage's scale. The level of SB was comparable in the three groups but the duration was different. The 75 micrograms clonidine was associated with 25% prolongation of SB at L2 and 29% prolongation of grade 3 MB Clonidine 150 micrograms prolonged the time of SB at L2 by 72% and grade 3 MB by 96%. Colloid infusion and the decrease in diastolic blood pressure were significantly greater in the clonidine 150 micrograms group compared to group I. A dose related prolongation of spinal anesthesia is demonstrated with clonidine.