Imatinib is a specific and potent inhibitor of the BCR-ABL tyrosine kinase. Several clinical trials have demonstrated the efficacy of imatinib in chronic myeloid leukemia. Adverse cutaneous reactions induced by imatinib are frequent and may be dose related. We report a case of an unusual pustular eruption in a patient with chronic myeloid leukemia, who received high doses imatinib for blast crisis and later voriconazole for invasive pulmonary aspergillosis. At the time of his skin eruption, elevated plasma levels of imatinib were recorded. Imatinib is primarily metabolized by the cytochrome CYP3A4. Voriconazole is a cytochrome CYP3A4 inhibitor and can lead to high plasma levels of imatinib. This case suggests that severe drug reactions to imatinib may be related not only to imatinib doses, but also to elevated plasma drug levels resulting from pharmacokinetic interactions. The monitoring of imatinib plasma levels may be of help for identifying patients at risk for severe toxicity.