Bioassays against the immature stages of the sweetpotato whitefly,Bemisia tabaci(Gennadius), were conducted with 0.2 and 2.0% aqueous solutions of neem-seed extract in laboratory and greenhouse studies. Cotton,Gossypium hirsutumL., foliage treated with neem-seed extract resulted in a reduction of egg viability and oviposition, prolonged larva periods, and larva mortality. Although the mode of action of the extract is unknown, we observed that adults were repelled, thus reducing oviposition. The failure of treated larvae to complete ecdysis would indicate an antiecdysteroid activity.