A new method has been developed for the rapid separation, purification and identification of triterpenoids from the seeds of the Neem tree (Azadirachta indica) and cell tissue cultures from it. The formation of triterpenoids in tissue culture was studied in collaboration with researchers at ENEA, Rome. Tissue culture samples prepared by them have been analysed for triterpenoids, in particular the natural insecticidal compound azadirachtin. A solid phase extraction method was developed for the partial purification of compounds from small quantities of tissue culture cells. Compounds were quantified using supercritical fluid chromatography. Azadirachtin was isolated from the tissue cultures of the plant for the first time, along with the related triterpenoids 3-acetyl-l-tigloylmeliacarpin, 3-tigloylazadirachtol and 3-acetyl-l-tigloylazadirachtinin. The decomposition of azadirachtin in solution at different conditions of pH and temperature was studied. The compound was most stable in mildly acidic aqueous conditions but readily decomposed in basic solutions. Azadirachtin decomposed more rapidly when heated in aqueous rather than in organic solutions. At room temperature, it was stable in organic solvents over a9 month period. At 90 °C in methanol, azadirachtin was quantitatively converted to 3-acetyl-l-tigloyl-azadirachtinin and 3-tigloylazadirachtol was converted to 11-dehydroxy-3-tigloylazadirachtinin. Methods were found to reduce the reaction time and increase the yield of salanninolide, isosalanninolide, nimbinolide and isonimbinolide, photo-oxidation products from salannin and nimbin. Isosalanninolide, a photo-oxidised product of salannin, was isolated from the seeds for the first time. This and other products were submitted for insecticidal tests. Studies with synthetic model compounds were made, in an attempt to understand the nature of the photo-oxidation reactions.