Inclusion Criteria:  Subject is treated with fluconazole for prophylaxis or treatment of an invasive fungal infection; Subject is 2 - 18 years of age on the day of the first fluconazole dosing Subject is managed with a central venous catheter or arterial line from which blood can be obtained.  Exclusion Criteria:  Subject is managed by means of an extracorporeal clearance technique; Subject has previously participated in this study.