  We study magnetotransport in conical helimagnet crystals. Spin dependent
magnetoresistance exhibits dramatic properties for high and low electron
concentrations at different temperatures. For spin up electrons we find
negative magnetoresistance despite only considering a single carrier type. For
spin down electrons we observe giant magnetoresistance due to depletion of spin
down electrons with an applied magnetic field. For spin up carriers, the
magnetoresistance is negative, due to the increase in charge carriers with a
magnetic field. In addition, we investigate spin dependent Hall effect. If a
magnetic field reaches some critical value for spin down electrons, giant Hall
resistance occurs, i.e., Hall current vanishes. This effect is explained by the
absence of spin down carriers. For spin up carriers, the Hall constant
dramatically decreases with field, due to the increase in spin up electron
density. Because of the giant spin dependent magnetoresistance and Hall
resistivity, conical helimagnets could be useful in spin switching devices.
