Most pharmacokinetic (PK) data of voriconazole have only been obtained after single dose and only in plasma (bound and unbound concentration). Regarding the pharmacodynamic activity it is more appropriate to determine the unbound concentration at the target site. The novel microdialysis technique allows to evaluate the concentration of voriconazole in subcutaneous interstitial fluid of tissue (unbound concentration), the compartment where most of the pathogens are considered to reside. Apart from multiple i.v. administration of voriconazole, sequence therapy has been introduced, i.e. a switch from direct administration into the systemic circu¬lation to an absorption based administration process, introducing further variability on the PK. A further important reason for assessing voriconazole concentrations during sequence therapy is that the i.v. dose is normalised to body weight but the oral dose is given independently of this demographic dimension.