Continuous haemo(dia)filtration techniques as a means of extracorporeal renal replacement therapy are being used more and more, especially on intensive care units. The effect of intermittent haemodialysis on the pharmacokinetics of systemic antibiotics is well documented and advice is provided in the drug data sheets regarding dosage, timing and additional doses (post haemodialysis). Continuous haemofiltration significantly alters the handling of these same antibiotics compared with haemodialysis, such that if the advice given for 'haemodialysis' is used for patients on haemofiltration, under-dosing the patient may lead to sub-therapeutic antibiotic levels. The reasons for these differences are discussed and suggested dosage modifications are given for commonly used antimicrobials based on available published data.