Infective episodes in immunocompromised children with indwelling central venous catheters were studied prospectively for one year. Culture of catheter hubs and skin at catheter entry sites during the first six months suggested that hub contamination was important in the pathogenesis of catheter colonization. The incidence of catheter-related bacteraemia, and possible catheter-related bacteraemia, fell by 56.5% following alterations in the protocol for manipulative care of catheters, from 5.82 per 1000 catheter days in the first six months to 2.53 per 1000 catheter days in the subsequent six months. A firm diagnosis of catheter-related bacteraemia was made simply and economically by a pour-plate quantitative blood culture technique. Attempts at eradication of catheter-related bacteraemia without removal of the catheter were successful in all cases.