In vitro studies have suggested a potential role for calcium channel blockers in manipulating the basic ionic defect of cystic fibrosis. In 17 adult patients with cystic fibrosis nicardipine was administered either intravenously or topically using iontophoresis or occlusive dressings. Sweat tests were performed before and after drug administration and examined using two way analysis of variance. No statistically significant difference was observed. We conclude that nicardipine used in vivo does not exert the easily demonstrable effect on the chloride ion defect that has been observed with other agents in vitro.