Within the ambit of the cyclic activity of the nasal mucosa the purpose of this study was to verify the existence of possible correlation between the rate of mucociliary transport (MCT) during the day and the circadian changes of the SIgA concentrations already found in a previous study. In the present work, a daily fluctuation of the SIgA concentrations was confirmed and it was shown that the values decrease from the greatest limit at 4.00 a.m. to the lowest at 10.00 a.m. Circadian changes of the MCT times are also shown. Moreover, the comparison of the data pertaining to these two parameters showed opposite patterns: when the mucociliary transport velocity decreases, the secretory immunoglubulins reach the highest levels. The phase-displacement of the two examined functions thus makes it possible to compensate cyclic impairments of one activity with contemporary improvement of the other.