Following several cases of Gram-negative bacteraemia secondary to intravenous heparin infusion contamination, we retrospectively reviewed nosocomial bacteraemias associated with heparin infusions at our institution. Thirty-one episodes of heparin-infusion related bacteraemia occurred in 30 patients over a 23-month period affecting 2% patients receiving heparin infusions for more than 48 h. Gram-negative bacteria were responsible for all bacteraemias. The care of infusions during clinical use was prospectively surveyed, revealing that approximately 20% of lines and cannulae were left for more than 72 h before replacement, and significant discordance occurred between line replacement and syringe and cannula exchange. We concluded that contamination of the infusions was probably extrinsic and secondary to manipulations of the system during use. Prolonged usage and discordant exchange of infusion components were likely important factors in initial contamination and subsequent bacterial proliferation. The problem resolved following the introduction of a policy for routine and simultaneous replacement of lines and syringes at 24-h intervals and upon cannula exchange.