An approximate dispersion relation for hydromagnetic waves is derived from the macroscopic equations of the plasma. Collision terms corresponding to collisions between electrons, ions, and neutrals are included in the macroscopic equations, and the three collision frequencies involved are retained in the approximation. Some simplification results from omission of certain terms in the macroscopic equations on the basis of an estimate of their relative magnitudes. An arbitrary direction of propagation is assumed in the derivation of the dispersion relation. The propagation constants for propagation parallel and normal to the magnetic field are represented by fairly simple expressions. There is good agreement between the numerical values of real and imaginary parts of the refractive index for these two directions of propagation and the various ionospheric heights computed from the approximative fomulas and from a more rigorous dispersion relation.