Nanotubes forming carbon atoms arrange differently, resulting into three main types of carbon nanotubes: armchair, zigzag, chiral. Thus, depending on their type, nanotubes may be regarded as chiral, molecular electrical conductors. As a consequence of symmetry arguments, the magnetoresistance of such tubes depends on the relative orientation of the traversing current and the external magnetic field. Magnetotransport measurements on single walled carbon nanotubes have been performed showing the expected dependence on both the current and magnetic field. Further, the quantum-mechanical model of a free electron on a helix in an external magnetic field is discussed in order to provide indicators to possible microscopic mechanisms.