The many methods so far developed for predetermining the regulation of alternators all depend on a theoretical approximation to the m.m.f. and flux distributions occurring under full-load conditions. In general, the better the approximation the more accurate (and more complicated) is the method. Estimation of the flux distribution is difficult owing to the different reluctances of the magnetic paths, and to saturation and leakage.The paper shows that a simple test may be carried out on an alternator at low speeds under such conditions that the m.m.f. and flux distributions of a given full-load case are reproduced exactly. The necessary conditions are readily calculated for any given machine, and only a relatively small output is needed from the prime mover.The method described in the paper is applicable to both single-phase and polyphase alternators an to cylindrical, salient-pole and inductor types. It may also be used to predetermine other alternator load-characteristics.The results obtained by the method, when compared with those of direct load tests, indicate that the errors are of the same order as the possible experimental errors.