The effects of Newcastle disease virus infection on the nasal mucociliary dysfunction after the mechanical stimulation, dehydration and cocaine application were investigated in the nonanesthetized in vivo chicken. Mucociliary transport rate and mucociliary wave frequency were measured simultaneously using the video monitor systems and electrophotometer connecting to the otomicroscope by the direct vision through the palatine cleft of the chicken which were placed in a specially designed plastic holder with mouth opener. Mucociliary transport rate was accelerated on the postnasal fossa adjacent to the mechanically stimulated side of the palatine cleft. The dehydration for 96 hours produced progressive decelerations of mucociliary transport rate, but not mucociliary wave frequency. Topical application of 20% cocaine to the postnasal fossa caused the ciliary paralysis within 5 minutes for more than one hour. The topical inoculation of Newcastle disease virus into the postnasal fossa induced the deceleration of mucociliary transport rate after 4 days and mucociliary wave frequency after 3 and 6 days significantly. We studied the effect of mucociliary transport rate and mucociliary wave frequency on the topical Newcastle disease virus inoculation after the mechanical stimulation, dehydration, and the application of 20% cocaine. Mucociliary transport rate in dehydration and cocaine groups were decelerated significantly 4, 7, 10, 13 days after inoculation, but not in the mechanical stimulation group. Mucociliary wave frequency in the dehydration group were decelerated significantly 3, 6, 12 days after inoculation, but not in the cocaine and mechanical stimulation groups. Therefore, the results suggest that the mucociliary dysfunction may increase and prolong the severity of viral infection.