Abstract Results of the investigation of the horizontal parameters of internal gravity waves with period >3 hours propagating at the mesopause region are presented. Wave disturbance registrations were carried out at station Maimaga (63°N, 129.5°E) by their influence on the intensity of the nightglow emission OH(7,3). Data obtained at bright moonless nights in winter 1982–1988 were used. Analysis of the 66 selected cases showed that the number of westward waves was greater than eastward ones, the mean value of eastward phase velocity exceeded the westward velocity mean value. It is shown that such horizontal phase velocity behavior can be the effect of the background wind filtration. A distribution of the averaged wave periods depends on the direction of propagation. Suggestions which could explain this effect are listed.