Abstract A narrow channel has been defined in a GaAs/AlGaAs heterojunction using metallic split gates formed by electron beam lithography. Resistance measurements have been performed at low temperature (1.2 K) and in magnetic fields of up to 8 T. By varying the negative voltage bias applied to the split gates it is possible to change the regime of electronic transport. In the low resistance regime, Shubnikov-de Haas (SdH) oscillations are observed which disappear as the resistance of the channel is increased. As the resistance is further increased towards the characteristic value of h e 2 , the conductance fluctuations become increasingly pronounced. In this paper, we discuss the experimental features observed in the magnetoresistance. both above and below this characteristic quantum resistance.