We present a new method for deducing the anisotropy vector Δ' of nonrelativistic particles in the solar wind frame. To order VSW/v, Δ'=-v-1[d ln F0(v)/d ln v> (VF-VSW), where v and F0(v) are the velocity and the mean velocity phase space distribution function, respectivity, of the particles in the spacecraft frame, VF is the bulk flow speed of the energetic particles in the spacecraft frame, and VSW is the solar wind speed. An illustration of the use of this equation is given from an interval during the upstream period before the April 5, 1979, interplanetary shock. ¿American Geophysical Union 1992