In addition to two previously reported Lupinus sericeus constituents, sparteine and β-isosparteine, 10,17-dioxo-β-isosparteine, a new natural product, and 17-oxosparteine, 10-oxo-β-isosparteine, and nuttalline (4β-hydroxylupanine) were also found in the aerial parts of this toxic range plant. Anagyrine, a suspected teratogenic constituent of this lupine for cattle, was not detected in the sample of this species under investigation. (-)-Sparteine exhibited the most potent acute toxic response for mice among the L. sericeus alkaloidal constituents tested.