ANUMBER of thin‐layer chromatography systems have been used to distinguish and identify some indole and oxindole alkaloids isolated from various species of the genus Mitragyna (Shellard & Phillipson, 1964). It has been suggested moreover that a relationship exists between the stereochemistry of these alkaloids and their behaviour on thin‐layer chromatograms (Phillipson & Shellard, 1966). Two new heteroyohimbine alkaloids, mitrajavine and hirsutine, have recently been isolated from Mitragyna species (Shellard, Beckett, Tantivatana, Phillipson & Lee, 1966) and their behaviour on thin‐layers has been compared with some related alkaloids of known stereochemistry. Based on this, certain suggestions have been made about the stereochemistry of these two new alkaloids. 1966 Royal Pharmaceutical Society of Great Britain