Antimicrobial therapy in hemodialysis patients is made possible by pharmacokinetic dosage modifications. The problem is that overdosage produces side effects whereas therapeutic drug action is missed by underdosage. The dose should be calculated to achieve identical peak levels (for bactericidal drugs) as in normal renal function or identity of AUC (for bacteriostatic drugs). Antimicrobial therapy is started with a loading dose which usually equals the dose in patients with normal renal function. The maintenance dose is reduced in renal failure and adjusted to the increase in the dominant elimination half-life. The effect of hemodialysis must be taken into account and replacement of the removed fraction by a supplementary dose is needed to assure therapeutic drug action.