Application of Dipel 2x at a rate of 250 glg was effective against the larvae of Spodoptera lit-toralis (1st to 4th instars), while larvae in older stages (5th and 6th instars) were more resistant. Lannate was highly effective against either young or old larvae. The addition of potassium carbonate to Dipel in-creased the larval mortality. In Sharkia governorate, the yield of soybean increased significantly when the infested areas were treated once by either Dipel 2x or Lannate with 1.113 fold increase compared with the control. In Alonoufia governorate, an obvious increase in soybean yield was also recorded when soybeans were treated three times with Dipel 2x or Lannete but the fold of increase was 2.031 - 2.066 times compa-red to the control. This difference in yield give a higher net profit to the farmer exceeding the costs of spray applications. J Islam Acad Sci 3:325-329, 1990 Key Words:B. thuringiensis, Lannate, S. littoralis.