A method for frequency stabilization of 3.39 μm He-Ne lasers, which makes use of the saturation dispersion of the v3 , P(7) methane transition is described. It is shown that with lasers which are stabilized by saturation effects, the absorptive and dispersive properties of the saturation resonance are not precisely distinguishable. This leads to a slightly asymmetric resonance and a shift of the apparent line-center. When using the dispersion for stabilization, the asymmetry can be detected and eliminated. Frequency stabilization to the true line center with an accuracy of 5 x 10-12 was attained