7-L-Glutamyl-Se-methylseleno-L-cysteine and Se-methylseleno-L-cysteine have been isolated from the seeds and leaves, respectively, of Astragalus bisulcatus. The glutamyl dipeptide was found to be the principal toxic compound in the seeds. Free Se-methylselenocysteine on a molar basis had toxicity similar to the dipeptide. It is suggested that the synthesis of these seleno amino compounds may be related to the ability of A. bisulcatus to assimilate large quantities of selenium without suffering from selenium poisoning.