The relative potency of lignocaine, bupivacaine and etidocaine was estimated by forearm skin weals in four volunteers. Potency was estimated as the time to half-recovery of a sharp sensation in response to a needle-prick. The increase in duration of action with increased concentration was greater for bupivacaine and etidocaine as compared with lignocaine. At the same concentrations, bupivacaine had a longer duration of action than etidocaine. However, etidocaine 1% had a longer duration of action than bupivacaine 0.5%.