Phytolacca dodecandra (L'Herit) grown in cell cultures was investigated for content of ribosome-inhibiting proteins, which was evaluated hy measuring inhibition of protein synthesis in a cell-free rat liver extract. Calli initiated from leaf, cotyledon, radicle, and hypocotyl and suspension cells initiated from leaf and cotyledon exhibited protein synthesis-inhibiting activity. Ribosome-inhibiting proteins were purified at least 14 times from suspension cells of P. dodecandra. The purified protein fraction contained two proteins as seen by sodium dodecyl sulphate polyacrylamide gel electrophoresis. The relative molecular masses were 30,000 and 31,000 and they showed a pI > 9.3. These new RIP's were shown to be different from dodecandrin with respect to molecular mass.