A continuing research programme of chemical control on major cotton pests in Thailand has been conducted since 1960 to discover the most effective insecticides. Before 1978 twelve systemic insecticides for controlling the cotton leafhopper,Amrasca devastans(Dist.), and the cotton aphid,Aphisgossypii Glov., and eight insecticides for controlling the cotton bollworm,Heliothis armigera(Hbn.), were identified and sent for official recommendation. This report gives details of research work carried out during 1978 and 1979, and includes seven new compounds, decamethrin, cypermethrin plus amitraz, sulprofos, profenofos, profenofos plus DDT, thiofanox and thiodicarb RH 0994, for bollworm control. The bollworm resistance to synthetic pyrethroids and the increase in whitefly,Bemisia tabaci(Genn.), after using the synthetic pyrethroids are also discussed.