Objectives The aim of this study was to prospectively evaluate the use of intraluminal ethanol for the prevention of catheter-associated bloodstream infection (CABSI) in immunosuppressed haematology patients. Patients and methods Patients receiving chemotherapy for haematological malignancy or haematopoietic cell transplantation were randomized in a double-blinded manner to receive either intraluminal 70% ethanol/water or heparinized saline locks on a daily basis throughout a prophylactic treatment period. The primary endpoint was an episode of CABSI (defined as ‘bacteraemia in a febrile patient with a central venous catheter that was in use within the preceding 48 h and with no other identified focus of infection’). The trial was registered with the Australian Clinical Trials Register: number ACTRN012605000383662. Results There were 34 and 30 prophylactic treatment periods in the ethanol and control groups, respectively. CABSI occurred in 3 (9%, 0.60/100 catheter-days) and 11 (37%, 3.11/100 catheter-days) prophylactic treatment periods in the ethanol and control groups, respectively (OR = 0.18, 95% CI 0.05–0.65, P = 0.008). Eleven (32%) and 5 (17%) patients in the ethanol and control groups, respectively, remained afebrile throughout the prophylactic treatment (P = 0.18). Conclusions The daily administration of ethanol locks into lumens of central venous catheters effectively reduces the incidence of CABSI.