In a companion paper a role is suggested for drift wave models in the theory of equatorial spread F. Here, some results of the collisionless theory of electrostatic drift waves are examined. The region of validity for a previously derived expression for the growth rate is determined. The region is then extended, and an expression for the growth rate is derived which is valid over a larger region including wavelengths much smaller than the ion gyroradius. The growth rate is maximum for k1&rgr;1?1.5. These results may have applications in a variety of space plasmas wherein steep gradients in plasma density occur.