The effect of ion drag on propagation of acoustic-gravity waves in an isothermal atmospheric F region is studied. The basic assumption is that ions move only along the magnetic lines of force with a velocity equal to the component of velocity of neutrals along the same direction. If the ‘collision’ frequency is constant as is the case near the F peak of the ionosphere, a general refractive index expression is derived. The refractive index is in general complex, indicating damping of the wave. Studies on two simple examples show that this damping is extremely large for gravity waves and still appreciable for acoustic waves. Further, this damping depends strongly on the direction of propagation. The angular preference on damping may be susceptible to experimental verification. For the case of varying ‘collision’ frequency, an exponential height-dependent model is studied. The resulting reflection coefficient shows that reflection can be appreciable if the collision frequency is not slowly varying over one vertical wavelength.