Two consecutive nonrandomized studies were conducted in children with prolonged granulocytopenia to evaluate the prophylactic antifungal activity of ketoconazole and the new triazole itraconazole. The conditions were equivalent in both studies. The incidence of colonization was 10% in the ketoconazole group and 19% in the itraconazole group (this difference is not significant). For suspected and proven infections, the incidence was 5% for ketoconazole and 10% for itraconazole, but the incidences were too low for statistical comparison. Although the colonization rate was higher for itraconazole, there was no sign of Aspergillus, whereas in the ketoconazole group an autopsy, proven aspergillosis has been reported.