This is a prospective, multi-center, open-label, repeat-dose pharmacokinetic study that contains two treatment (micafungin 1.0mg/kg and 1.5mg/kg) dose groups. Subjects will be enrolled according to age and stratified by weight to receive either 1.0mg/kg (weight \> 25kg) or 1.5mg/kg ( weight \< 25kg) micafungin.
Children (4 months to \< 2years, 2 to 5 years and 6 to 11 years) and adolescents (12 to 16 years) undergoing HSCT who require antifungal prophylaxis will be enrolled