With a view to identifying and understanding the genotypic differences in yield under terminal drought, a range of lupin genotypes representing narrow-leafed lupin (Lupinus angustifolius L.) and yellow lupin (Lupinus luteus L.) was studied in field experiments in the low rainfall Mediterranean environment of Western Australia over 3 seasons. In each year Merrit, the most common commercial cultivar in Western Australia, was used as the reference to which the yield of other genotypes was compared. In the first and third year, 5 or 6 genotypes were grown with and without irrigation from the start of pod set. In the second year, 9 genotypes were grown with irrigation and under a rainout shelter from the start of pod set. Detailed measurements were made of plant water status, leaf area and biomass production, flowering and podding date, and seed yield and its components.The timing and intensity of the terminal drought varied from average in 1998 and 1999 to extreme in 2000. Post-podding leaf water potential(Psi(leaf)) under rainfed conditions decreased to -2 MPa in 1998 and 1999 and below -2.5 MPa in 2000, whereas under supplementary irrigation it was maintained at -1.2 MPa in 1998 and 1999 and at -1.5 MPa in 2002.The seed yield of all genotypes under terminal drought varied from 24 to 66% of that with supplementary irrigation. In each year, the seed yield under rainfed conditions showed genotypic differences consistent with the timing and intensity of the development of terminal drought. Under conditions of terminal drought the seed yields of the narrow-leafed lupin cultivars Belara and Tallerack, and of the breeding line WALAN 2049, were higher than of Merrit by 29% in 1998. Tanjil, Belara, and Quilinock out-yielded Merrit by 33-53% in 1999 and Belara and Quilinock out-yielded Merrit by 80% in 2000. Harvest index was higher in Belara and Quilinock than in Merrit. Under both terminal drought conditions and supplemental irrigation, Belara and Quilinock had high seed yields that were associated with a greater number of seeds per pod and larger seed size. It is argued that early flowering and podding in Belara and Quilinock allowed more seeds to develop and fill before the terminal drought became more severe.