Thirty-three patients undergoing elective transurethral resection of She prostate were allocated randomly to receive either 0.9% isotonic saline 7mlkg(-1) (16 patients), or 3% hypertonic saline 7mlkg(-1) (17 patients) as a preload before spinal anaesthesia. After spinal anaesthesia, the incidence of systolic arterial pressure < 75% of control value was greater in the normal saline group than in she hypertonic saline group. Also, the mean dose of phenylephrine required to maintain arterial pressure > 75% of the baseline value was significantly greater in she normal saline group than in the hypertonic saline group.