Two groups of Archaean orthogneisses from the Western Gneiss Terrain, approximately 100 km east of Perth, Western Australia, give Nd model ages of 3150 Ma to 3240 Ma, and 2950 Ma to 3050 Ma respectively. A Sm-Nd whole-rock isochron of 3210 ± 190 Ma (2σ), obtained by including a mafic granulite with samples having the older group of model ages, is in close agreement with U-Pb zircon ages of Nieuwland & Compston (1981). This agreement, together with a chondritic initial 143Nd/144Nd, indicates a limited prior crustal residence time (<200 Ma) for the gneiss protoliths. Leucosome and melanosome components of nearby migmatite yield significantly younger Nd model ages of 2860 Ma and 2660 Ma, respectively. Post-tectonic granites also give younger model ages of 2770 Ma and 2680 Ma, consistent with... the addition of new material to the continental crust at this time. When contrasted with Nd model ages of 3630 Ma and 3510 Ma from the northern extension (de Laeter et al., 1981) of the Western Gneiss Terrain, these results indicate that this is a composite belt with an igneous and metamorphic history spanning almost 1000 Ma. Comparison with isotopic results for gneisses from the eastern margin of the Yilgarn Block indicates that the Western Gneiss Terrain is fundamentally older, suggesting a dominant pattern of crustal growth from west to east.