In the present study we investigated the influence of two common air pollutants, sulfur dioxide (SO2) and nitrogen dioxide (NO2) on ciliary beat frequency (CBF). Ciliated cells were obtained by nose brush from 12 healthy volunteers and placed on a polycarbonate membrane which was in contact with Ringer's electrolyte solution. This allowed the supply of the cells by capillarity in parallel to the reaction of the pollutants with the cell surfaces. In an exposure chamber the cells were exposed for 30 min. at 37 degrees C either to SO2 (2.5-12.5 ppm) or to NO2 (3.0-15.0 ppm), or to a mixture of NO2 (12.0 ppm) and SO2 (2.5 or 5.0 ppm). CBF was measured by video-interference-microscopy. With SO2 we observed a dose-dependent decrease in CBF with Ringer's solution. 2.5 ppm SO2 caused a 42.8% decrease and 12.5 ppm a decline of approximately 100% (8.10 +/- 0.24 Hz vs. 0.28 +/- 0.20 Hz). In parallel, we observed a decrease in the pH-value from 7.4 to 3.6. 30 min. NO2 exposure (3.0-15.0 ppm) induced a significant dose dependent increase in CBF from 8.4 +/- 0.34 Hz to 9.4 +/- 0.44 Hz. Exposure to a mixture of SO2 and NO2 with Ringer's solution revealed that SO2 exerts a stronger influence on CBF than NO2. Exposure to both pollutants resulted in the same as exposure to SO2 alone. Our findings demonstrate a strong correlation between SO2-modified pH values and CBF. Exposure to a combination of two pollutants revealed the dominant influence of SO2 on CBF while the augmented effect of exposure to NO2 alone might be due to the oxidative potential of this gas.