Topical application of RNA and protein synthesis Inhibitor, cydoheximide (3;2 (3,5-Dimethy1-1-2-oxocydohecyl) -2-hydroxy ethyl glutarimide) to 0-24 H-old fourth instar female nymph, Schistocetra °regatta (Forskal) revealed that, biological activities are dose dependent. This treatment induced three types of responses: the high doses resulted in different percentages of the permanent fourth instar nymphs, the low doses produced precocious adults, meanwhile the lower doses, especially 30 pg/insect, inhibited the metamorphosis completely. C16-)H extra cydohedmide therapy restored the normal development and metamorphosis of the resulting fifth instar nymphs, which confirm that the last two types of response are related to juvenile hormone (3H) deficiency as a result of anti-3H action of cydoheximide. On the other hand, the lowest doses of this compound (20, and 10 pg /insect) had produced the solitary green colour in the resulting fifth instar nymphs, that considered as an indicator for the high level of 3H in their haemolymph. Owing to these obtained results agreed with the dual effect of anti-)H (precocene 11), cydoheximlde acts as anti-JH in S. gregatia.