Voriconazole (VCZ), the antifungal drug active against Candida and Aspergillus is a substrate of CYP2C19, whose proportion of poor metabolizers is about ~20% in Asian population. The AUC's of VCZ differs over 4 folds by CYP2C19 genotypes of homozygotic wild type, heterozygote, and homozygotic poor metabolizers. The Asian population enrolled in the metabolism of VCZ were mainly Japanese and Chinese, without Korean subjects. The proportion of poor metabolizers in Korean population is known to be around 12% (Pharmacogenetics. 1996 Dec;6(6):547-51). The importance of CYP2C19 genotypes on the pharmacokinetics (PK) of voriconazole is well established, Hence, it is desirable to individualize the dosage regimen of VCZ according to the genotypes of patients. Fungal infection in immunocompromised patients is a life threatening condition which needs critical care. Although the PK change by genotypes are well known, its clinical implication or need for different dosage regimen by genotypes is not established, yet.