Voriconazole is a new antifungal agent effective in the treatment of invasive aspergillosis. Interpatient variation in plasma concentrations is considerable-more than 100-fold. We describe 3 patients with diverse manifestations of toxicity ( e. g., hallucinations, hypoglycemia, electrolyte disturbance, and pneumonitis) possibly attributable to high voriconazole concentrations. Measurement of plasma concentrations could be helpful in optimizing voriconazole dosages.