Several antimicrobial drugs have been shown to pharmacokinetically interact with cyclosporine. On two separate occasions, we observed increases in cyclosporine plasma concentrations during concomitant miconazole therapy in a heart transplant patient with an infection secondary to Pseudallescheria boydii. To our knowledge, no interaction between cyclosporine and miconazole has previously been reported. In addition, drug interactions were observed between cyclosporine and ketoconazole and possibly between cyclosporine and SCH 39304, an investigational azole-antifungal agent. No interaction was noted between cyclosporine and fluconazole. In general, clinicians should anticipate drug interactions between cyclosporine and azole-antimycotic agents.