Impaired cell membrane chloride ion movement in cystic fibrosis results in reduced resorption of sodium and chloride from sweat gland ductules producing the high concentrations measured in the sweat as a diagnostic test. Normal chloride ion movement can be restored in vitro by blocking transepithelial calcium flux with lanthanum, suggesting a potential role for calcium channel blocking drugs in the management of cystic fibrosis. We studied the effect of nicardipine, a calcium channel blocker, on the sweat sodium in 17 adult patients with cystic fibrosis. Nicardipine was administered intravenously or topically using iontophoresis or occlusive dressing. No significant change in sweat sodium concentration was observed between pre- and post-drug administration. We conclude that nicardipine used in vivo does not exert the same effect as lanthanum demonstrates in vitro on transepithelial cell membrane chloride ion movement in cystic fibrosis.