The effects of two sympathomimetic drugs on mucociliary activity and mucosal blood flow in the rabbit maxillary sinus were investigated by using a photo-electric technique (mucociliary activity) and laser Doppler flowmetry (blood flow). The responses produced were compared with effects of ligation of the external carotid artery. The alpha 1-agonist phenylpropanolamine (0.1-100 micrograms/kg) had no effect on the mucociliary activity, whereas the blood flow was reduced by 33.8 +/- 8.9% (mean +/- SE) when the dose was 100 micrograms/kg. The alpha 2-agonist xylometazoline (0.01-10.0 micrograms/kg) reduced mucociliary wave frequency by 21.6 +/- 4.6% (mean +/- SE) (maximum) for the dose 10 micrograms/kg. The blood flow was reduced by xylometazoline in the interval 1.0 to 10.0 micrograms/kg, with a maximum decrease of 65.8 +/- 2.6% (mean +/- SE) for the dose of 10 micrograms/kg. Ligature of the external carotid artery reduced blood flow by 76.0 +/- 4.6% (mean +/- SE), but did not significantly influence the mucociliary wave frequency. It is concluded that the decrease in mucociliary activity induced by alpha 2-adrenoceptor agonists is not due to a reduced blood flow.