A departmental survey indicated that the large majority of anaesthetists believed that injection of local anaesthetic before insertion of an intravenous cannula was unnecessary if a cannula of 18 gauge or smaller was used, because injection of local anaesthetic would be more painful than insertion of the cannula. A study was undertaken to test this hypothesis. The results showed that intravenous cannulation with a cannula of 18, 20 or 22 gauge was significantly (p less than 0.006) more painful than a subcutaneous injection of 1% lignocaine. We recommend that subcutaneous injection of local anaesthetic should be considered before insertion of any size of intravenous cannula.