1. Proteins extracted from the seeds of the Euphorbiaceae croton tiglium and Jatropha curcas were separated into three major peaks (I, II, and III) by Sephadex chromatography. 2. The crude protein from both seeds and peaks I and II from Croton and peak I from Jatropha were toxic to mice, to different extents. 3. The crude protein and peak I and peak II from both seeds, inhibited protein synthesis by a reticulocyte lysate; maximum inhibition was exerted by peak II from both seeds. None of these preparations affected protein synthesis in vitro by Ehrlich ascites cells.
