The well known and most useful property of the neem tree is the antifeedant property to insects expressed even in crude extracts. Azadirachtin has the highest biological activity and in addition to antifeedant property, it also produces developmental abnormalities in almost all insect orders. The chemical structure of azadirachtin has been determined unequivocally and the radio labelling opened the possibility of biochemical, metabolic and autoradiographic studies. The timing and titre of the two morphogenetic hormones are altered leading to loss of coordination of developmental events. This effect on morphogenetic hormones could be traced as the influence of azadirachtin on the neuroendocrine system which secrete the tropic hormones that eventually control the activity of corpora allata and prothoracic glands. Recent studies have shown that turnover of the neurosecretory material is poor in azadirachtin-treated insects leading to derangement of the hormonally controlled development.