Radio-echo sounding data are used to investigate bed roughness beneath the three enhanced-flow tributaries of Slessor Glacier, East Antarctica. Slow-moving inter-tributary areas are found to have rough beds, while the bed of the northernmost tributary is relatively smooth. A reconstruction of potential subglacial drainage routing indicates that water would be routed down this tributary, and investigations of basal topography following isostatic recovery reveal that the bed would have been below sea level in preglacial times, so marine sediments may have accumulated here. Together, these factors are further support for the dominance of basal motion in this tributary, reported elsewhere. Conversely, although the other two Slessor tributaries may have water routed beneath them, they would not have been below sea level before the growth of the ice sheet, so cannot be underlain by marine sediments. They are also found to be rough, and, within the range of uncertainties, it is likely that basal motion does not play a major role in the flow of these tributaries. Perhaps the most interesting area, however, is a deep trough where flow rates are currently low but the bed is as smooth as the northern Slessor trough. It is proposed that, although ice deformation currently dominates in this trough, basal motion may have occurred in the past, when the ice was thicker.