An expression for the equilibrium diffusion rate is derived using the generalized equations previously published. Different limiting forms of this expression are compared with the intermediate collisional and highly collisional results derived earlier. The validity of these results are found to be more restricted than previously assumed. To cover the range of experimental interest, two new limiting conditions are considered. In both these the ambipolar diffusion is generally comparable to the Pfirsch‐Schlu¨ter rate. The generalized expression allows the diffusion to be evaluated in the transition zones between the different regimes.