Nasal mucociliary transport was measured in a group of 30 adult patients (eight women and 22 men; age range 21-78 years, mean 47.9 years) treated with hyperbaric oxygen (HBO) therapy and in a control group of 32 adult subjects (two women and 30 men; age range 20-50 years, mean 32.0 years) compressed in a hyperbaric chamber without oxygen therapy. The treated patients breathed 100% oxygen at 250 kPa pressure for 60 min. Subjects from the control group were compressed in the hyperbaric chamber at 250 kPa for 70 min. Nasal mucociliary transport was measured with the saccharin clearance test. After exposure to HBO, the nasal mucociliary transport time was significantly decreased by 26% (P < 0.01) and returned to the original value after 24 h (increased by 8.3%, P = 0.25). In the control group, compressed in air, there were no statistically significant changes. This study shows that simultaneous compression and pure oxygen cause an increase in nasal mucociliary transport. The mechanism of activation of mucociliary clearance is probably the increased oxygenation of blood plasma and enhancement of metabolism in ciliated epithelium.