[en] The stability of non-relativistic runaway electron distributions with respect to the anomalous Doppler resonance is examined in a range of parameters of interest to tokamaks, i.e., for Y identical to ω/sub pe//Ω/sub ce/ ≤ 2 and for ohmic electric fields ε identical to E/E/sub c/ ≤ 0.1. Distribution functions are calculated numerically within a region up to 35 v/sub e/ (thermal velocities) using a finite-element 2-D Fokker-Planck code. Alternatively, an analytic approximation for the runaway distribution function is used, valid beyond the critical velocity v/sub c/ ≅ v/sub e/ (E/sub c//E)/sup 1/2/. Stability thresholds in (ω, k/sub parallel/) - space are then determined