Infusion thrombophlebitis is the commonest complication of intravenous cannulation. This study was undertaken to prospectively evaluate a double-occlusive dressing technique and a new cannula, bismuth oxide-Teflon (Critikon Inc., Aust.), comparing it to Vialon (Deseret Medical Inc., Utah, USA). The study group of two hundred patients had a 16 gauge intravenous cannula inserted in theatre using a standard technique. The incidence of thrombophlebitis was determined on a daily basis. Cannula tips were sent for culture on removal. Vialon was found to be superior to Teflon after day 1. Although a double-occlusive dressing technique increased the duration of cannulation (50.9 vs. 41.9 hours, P less than 0.05), there was no difference in the incidence of thrombophlebitis. Neither cannula material nor dressing technique had an influence on the results of cannula tip culture (6% incidence). There was no evidence of bacteraemia in any case.