The recombination probability of geminate triplet radical ion pairs at single encounter alpha has been determined by means of the proposed method of experimental data processing based on the Noyes theory regarding the Onsager concept. The method is based on measuring magnitude of magnetic field effect in the yield of the geminate recombination products of triplet pairs depending on medium viscosity. The method was used to determine alpha for the recombination of geminate triplet radical ion pair {pyrene(-)+N,N-diethylaniline(+)}(3) in methanol. It amounts to 10(-4), which is four orders of magnitude smaller than that obtained by the standard kinetic method. This is the basis upon which to conclude that even with the account of Onsager correction for polar media the use of Noyes theory for alpha determination is incorrect.