<jats:p> Extracts of <jats:italic>Euphorbia esula</jats:italic> L. and <jats:italic>Croton tiglium</jats:italic> L., two members of the Euphorbiaceae which have been used widely in folk medicine for treating cancers, showed antileukemic activity against the P-388 lymphocytic leukemia in mice. Systematic fractionation of the extract of <jats:italic>Euphorbia esula</jats:italic> L. led to characterization of a major antileukemic component as the new diterpenoid diester, ingenol 3,20-dibenzoate. Similar fractionation of <jats:italic>Croton</jats:italic> oil led to characterization of phorbol 12-tiglate 13-decanoate as an active principle.