The variation of alpha, the ratio σc/σf, has been determined for U235 and Pu239 as a function of position in EBR. Samples of U235 and Pu239 were exposed in the core, inner blanket, and outer blanket; the samples were analyzed radiochemically to determine the fraction fissioned and mass spectrometrically to determine the fraction which had undergone the capture process. The vertical and horizontal patterns of capture and fission probability have been determined. The variation of η in the reactor has been plotted, assuming that remains constant.