The effect of topical application of juvenile hormone analogues farnesyl methyl ether and kinoprene (ZR 777) at different doses to eggs immediately after laying, germ band formation and blastokinesis, produced different types of abnormal embryos with varying degrees of derangement of development, most of them ultimately resulting in failure to hatch. Some of the embryos were almost normal but failed to hatch even though they continued to develop inside the chorion and died two days later. On the whole, there was correlation between dose of the analogue applied and mortality rate. Kinoprene was much more effective than farnesyl methyl ether. With given dose, per cent embryonic mortality was more or less the same whether the analogues were applied just after oviposition or germ band formation, but was lesser when applied immediately after blastokinesis. The period just after germ band formation appeared to be most sensitive. Treatments affected the endocrine system. The neurosecretory index was higher in the treated embryos. Prothoracic glands and their nuclei showed considerable enlargement in treated embryos continuing development inside chorion even after their controls hatched. The corpus allatum was smaller in treated embryos and corpora cardiaca were filled with neurosecretory material. Cuticle development was abnormal after treatment.