The Hall effect has been measured on pure alpha and beta plutonium and on a 3.4 at.% aluminum-stabilized delta-phase alloy. Measurements were made between 6 and 438°K with magnetic fields up to 21 kG. In each phase, Ro is positive and relatively independent of temperature at higher temperatures, but shows strong temperature dependence at low temperatures. Ro for alpha plutonium becomes negative at 185°K and goes through a minimum at 23°K. The Ro's for beta plutonium exhibit a maximum at 29°K and then drop sharply to negative values below 17°K. The value remains positive, with no maximum, for the delta alloy throughout the temperature range. The data were used to test a two-band model, and were found to fit best to a nearly full 7s band and empty 5f band. Because of similarities with data on the rare-earth metals, the low-temperature behavior of Ro for each phase is thought to be due to antiferromagnetic ordering, but the anomalies in the electrical resistivity of the three phases are probably due to interband scattering.