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.

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