Children in the study will be hospitalized for 21 days. They will receive voriconazole twice a day (every 12 hours) for 8 days, infused through a vein over a period of 1 to 2 hours. The dose will be determined based on the individual child's weight. Blood samples will be collected at various intervals before and after the infusions on days 1, 2, 4 and 8 to determine the amount of drug in the blood. On day 8, the child will have another physical and eye examination, as well as additional blood and urine tests. If additional treatment is required, voriconazole may be continued for up to day 21. (Children who require the drug for more than 21 days may receive it under another research protocol.) On the last day of treatment, the child will have another physical examination, and blood and urine tests. These procedures will be repeated again at 30 to 35 days following the last dose of drug. A small sample of blood will also be analyzed for genetic information related to the rate of metabolism of voriconazole-that is, how fast or slow it is cleared (eliminated) by the liver.