The spread of lumbar epidural analgesia was studied in 48 old urological patients (56-81 years). Bupivacaine 0.5% 20 ml was injected at either 1 ml/s with a Tuohy needle with the bevel directed cephalad (Group I) or caudad (II) and at 0.22 ml/s directed cephalad (III) or caudad (IV). Immediately after injection, the patients moved from a sitting to a horizontal position and analgesia was tested every 2 min by skin pin-prick. At 10 min, there were differences in the mean caudad spread; the greatest spread in Group II was 4.5 segments and the smallest in Group III 2.4 segments, not significant (n.s.). The differences became smaller with time and the maximal spread after 30 min was similar in all groups. In six patients, who all belonged to either Group I or Group III (bevel cephalad), skin analgesia did not reach the S 5 segment. One of the Group I patients developed a transient motor paralysis of the lower extremities immediately upon injection. All patients recovered completely from the block and no toxic reactions were observed. The duration of the block and the accompanying fall of blood pressure were similar in the different groups. The mean venous blood levels of bupivacaine were highest in Group III and lowest in Group I (n.s.). The highest individual bupivacaine blood level was 1.25 micrograms/ml 30 min after injection, while generally the highest concentrations appeared at 20 min after injection. The study indicated a lack of significant difference on varying the speed of injection or turning the Tuohy needle, but it has to be emphasized that this may apply only to bupivacaine, which has distinct physicochemical properties, and also to old patients with an age-dependently modified epidural space.