Effect of high magnetic fields on the charge-density-wave state in NbSe3

We present a systematic study on a large magnetoresistance in NbSe3 as a fu nction of temperature under various pressures. The large magnetoresistance below T-c2 is observed as long as the T-c2-CDW phase exists. However, when the T-c2-CDW phase is suppressed totally by high pressure and the supercond ucting phase is induced at the same time, no anomaly, including the large m agnetoresistance, is induced by a magnetic field up to 12 T. The origin of the large magnetoresistance is discussed by considering normal carriers on the ungapped Fermi surface created on the CDW transition and comparing this magnetoresistance with the pressure-induced magnetoresistance that is newl y observed above T-c2.