In eastern Ireland, subglacial bedforms including drumlins and Rogen moraines were modified by headward erosion along two ice streams which had over- lapping flow tracks.The ice streams, which hadtidewater termini, are dated by geochrono- metric and morphostratigraphic methods to 5 15.0 14 Ckyr BP &Castleblaney ice stream) and � 13.8 14 Ckyr BP &Armagh ice stream). Bedforms along ice-stream tracks show a morphological continuum which reflects a down-ice increase in the degree of modification by ice-stream activity &i.e. resulting in unmodified ! remoulded/overprinted ! cross- cut ! streamlined bedforms).The down-ice changes inbedform types are inferred to relate to changes in subglacial drainage and sediment-transport mechanisms. Bedform and sedi- mentary evidence suggest that discrete subglacial meltwater channels which developed up- ice changed in a down-ice direction to unchannelized flows which deepened towards the ice margin. Meltwater release from subglacial cavities, and produced by strain heating at sheared ice-stream margins, probably helped support ice-stream flow, which ended as the volume of subglacial meltwater discharge decreased. Dated millennial-scale cycles of ice activity may be related to instability at tidewater margins, followed by complex thermal and hydraulic responses within the ice mass.