Objectives: We investigated the effects of oxymetazoline hydrochloride on the regulation of healthy human nasal ciliary beat frequency (CBF) and its influence on nasal mucociliary transport time (MTT). Methods: Changes in (cultured) human nasal CBF in response to increasing concentrations of oxymetazoline within 20 minutes were quantified by use of high-speed digital microscopy. Moreover, the MTT before and after application of 0.05% oxymetazoline was determined by use of the saccharin test. Results: Whereas no statistically significant difference was identified when compared to basal CBF at the concentration of 0.025% or 0.05%, both 0. 10% and 0.20% oxymetazoline induced a significantly lower CBF at the end of the observation period. The decrement induced by 0.20% oxymetazoline appeared earlier. At concentrations ranging from 0.025% to 0.20%, the inhibitory effect was dependent on the concentration of oxymetazoline. In addition, the use of 0.05% oxymetazoline increased the mean (+/- SD) human nasal MTT from 474 +/- 21 seconds to 572 +/- 41 seconds (n = 29). Conclusions: The clinical concentration of oxymetazoline, 0.05%, has no obvious inhibitory effect on human nasal CBF in vitro. The increased MTT caused by 0.05% oxymetazoline in vivo is within the normal range.