Spinal anesthesia with two types of 0.5% bupivacaine hydrochloride solution, isobaric AJ-007 I and hyperbalic AJ-007 H, was studied clinically in 106 surgical patients with collaboration of 7 university hospitals. The following results were obtained. 1) Successful analgesia with motor block on abdominal wall and legs could be induced by dosages of 2.0 ml, 3.0 ml and 4.0 ml of either of the two solutions. 2) With isobaric solutions, the duration of the block was prolonged dose dependently. Anesthetic levels tended to increase and onset times of the block tended to decrease, with increasing dosage. 3) Hyperbalic solutions tended to produce higher levels of the block more rapidly. However, the duration of the block seemed to be shorter than that achieved by isobaric solutions. 4) The incidence of hypotension and bradycardia was similar to that observed in ordinary clinical spinal anesthesia. In one young male, a high level (C 2) of anesthesia was achieved after administration of 4.0 ml of hyperbaric solution. This patient was managed uneventfully under general anesthesia during the surgery. These results indicate that these two solutions of 0.5% bupivacaine are useful for spinal anesthesia.