['To determine the effect of oral clonidine premedication on duration of sensory and motor block, postoperative analgesia, hemodynamic stability, sedation, and respiratory parameters after subarachnoid anesthesia (SA).', 'Prospective, double blind, randomized, placebo-controlled study.', '80 ASA physical status I patients were randomized into four equal groups to receive oral premedication with either clonidine 5 mcg/kg (C5), clonidine 2.5 mcg/kg (C2.5), diazepam 100 mcg/kg (D), or placebo (PL).', 'The following parameters were measured: duration of motor and sensory block, requirement for postoperative analgesia; systolic (SBP), diastolic (DBP), and mean (MBP) blood pressures; heart rate (HR); sedation and anxiolysis scales; respiratory rate (RR); oxyhemoglobin saturation; and complications. (1) The duration of sensory and motor block did not differ significantly among the groups. (2) There were no differences in the time to first request for analgesia and in requirements for analgesia in the first 24 postoperative hours. (3) Clonidine premedication before SA did not produce episodes of significant hypotension. HR did not differ significantly among the groups. Baseline SBP was significantly higher (p = 0.037) in group PL than in groups C5 and C2.5. Three minutes after SA significant decrease in the following parameters was observed: SBP in group PL compared with the other three groups (p = 0.004), DBP in group PL vs. groups C5 and C2.5 (p = 0.002), and MBP in group PL vs. groups C5 and C2.5 (p = 0.003). (4) Sedation and anxiolysis were more pronounced (p = 0.0001) in groups C5 and C2.5 than in groups D and PL and in group C5 than in group C2.5. (5) RR was significantly lower (p = 0.0024) in group C5 than in groups D and PL. (6) Complications consisted of three episodes (15%) of bradycardia in the C5 group and two of bradypnea (10%) in the same group.'] Does oral clonidine premedication prolong analgesia after herniorrhaphy under subarachnoid anesthesia?