A further range of Strophanthusoils has been examined. All contain 9-hydroxyoctadec-12-enoic acid (6-15%) and may also contain minor amounts (≯0.1%) of erythro-9 : 10-dihydroxystearic acid. The estimation of hydroxy esters by the quantitative infra-red spectroscopic method is discussed and the optical rotations of the unsaturated hydroxy acid and some of its derivatives are reported.