SUMMARY Lumbar epidural blockade has been used in a series of 659 patients to compare the analgesic properties of lidocaine and prilocaine. Solutions of both compounds were compared as hydrochloride salts in 2% and 3% concentration with and without adrenaline 1:200,000. Solutions of base, made soluble by equilibration with carbon dioxide at a pC02 of 700 mm Hg were also compared in concentrations of 1.75% for lidocaine and 1.71% for prilocaine. Comparisons were based on measurements of latency, spread of analgesia, intensity of motor blockade and duration of analgesia. The quality of blockade in all the test solutions was increased by the addition of 1:200,000 adrenaline. Prilocaine has a slow latency compared with lidocaine, but in plain solution its duration is longer than that of lidocaine. The 3% hydrochloride solutions have no practical advantage over die 2% solutions for epidural blockade. Analgesia resulting from the C02‐base solutions is superior in every respect to the blockade produced by equivalent concentrations of the hydrochloride salts.

Relationship) of height and segmental dose for 2 per cent solutions in 155 normal patients between the ages of 20 and 81 years (supine position).

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Varying concentrations of lignocaine between 1 and 5 per cent with and without adrenaline 1/200,000 were used for epidural analgesia in 255 patients. Measurements were made of latency of onset, degree of segmental spread, intensity of motor blockade and duration. The segmental spread of analgesia depended on the mass of solute injected and not on the volume, and at any given age the relationship between dose and area of segmental blockade was constant for all concentrations between 2 per cent and 5 per cent. Lignocaine in 1 per cent concentration blocked more spinal segments than the stronger concentrations, but produced a blockade of weaker intensity and shorter duration. Adrenaline 1/200,000 did not appear to affect the area of segmental spread appreciably, but it doubled the duration and trebled the intensity of motor blockade in all concentrations tested. Latency of onset was irregularly affected by concentration and by addition of adrenaline. Analgesia developed fastest with 1 per cent and 5 per cent plain lignocaine, and with 3 per cent lignocaine with adrenaline, while 1 per cent and 5 per cent lignocaine with adrenaline gave the slowest onsets.