Human respiratory tract epithelium suitable for measuring ciliary beat frequency (CBF) may be obtained by nasal brushing. We have used such ciliated epithelium in an in vitro preparation to study the effects on CBF of lidocaine hydrochloride administered topically in vivo before brushing or in vitro after brushing. Beat frequency measured after in vivo administration was unchanged compared to control values while incubating ciliated epithelium in vitro in increasing concentrations of lidocaine resulted in dose-related cilioinhibition. Drug concentrations required to depress ciliary activity in vitro were much higher than those occurring in clinical practice.