Certain calcium channel blockers such as diltiazem, nicardipine, and verapamil, but not nifedipine, are known to raise blood levels of cyclosporin A (CsA) upon concomitant administration. Isradipine, a newer calcium channel blocker purportedly free of interaction with CsA metabolism, was utilized for blood pressure control in a patient with Sézary's syndrome being treated with CsA. Unexpectedly, indirect evidence of a drug-drug interaction occurred with alterations in CsA blood levels dependent upon continuation/discontinuation of isradipine. Although a single case, this report underscores the necessity for monitoring CsA blood levels in patients being treated with other drugs in order to avoid deleterious side-effects secondary to altered CsA levels.