Onset (defined as the time between injection and achievement of the highest level of sensory blockade), duration, and regression of sensory and motor blockade after the intrathecal administration of 3 mL plain bupivacaine 0.5%, previously equilibrated to either 37 degrees C or 20 degrees C, were studied in two groups of 20 patients. In patients receiving the solution equilibrated to 37 degrees C, the maximum level of sensory blockade was significantly higher (T 4.6 vs T 7.5), variability was smaller (SEM 0.33 vs 0.58), and duration of the sensory level of blockade at or above T 6, T 8, and T 10 was significantly longer (56 min vs 20 min, 101 min vs 59 min, and 131 min vs 77 min, respectively). There were no significant differences with regard to onset of sensory and motor blockade or either the time needed both for the sensory level of blockade to regress two segments from its highest level and to the first lumbar segment, or the duration of complete motor blockade of the lower limbs. It is concluded that the intrathecal administration of a bupivacaine solution previously equilibrated to 37 degrees C as compared with a solution injected at room temperature results in a higher, more predictable maximum sensory level of blockade with longer duration at or above T 6, T 8, and T 10.