Nine compounds were tested on mature tobacco plants as foliage sprays for the control of the early instars of the tobacco hornworm, Manduca sexta (Johannson), and the tomato hornworm, M. quinquemaculata (Haworth). Three systemic insecticides, NIA 10242 (2,3-dihydro-2,2-dimethyl-7-benzofuranyl methylcarbamate), American Cyanamid CL-47470 (cyclic propylene (diethoxyphosphinyl)-dithioimidocarbonate), and Amer. Cyan. 47031 (cyclic ethylene (diethoxyphosphinyl) dithioimidocarbonate) were the most effective materials tested. Oxydemetonmethyl was ineffective in controlling hornworms. Five nonsystemics, Chipman RP-11974 ( O, O -diethyl phosphorodithioate S -ester with 6-chloro-3-(mercaptomethyl)-2-benzoxazolinone), GS-13005 ( O, O -dimethyl phosphorodithioate S -ester with 4(-mercaptomethyl)-2-methoxy-∆2-1,3,4-thiadiazolin-5-one), GC-9160 (ethyl 1,1a,3,3a,4,5,5,5a,5b,6-decachloro-octahydro-2-hydroxy-1,3,4-methane-2 H -cyclobuta[ cd ]pentalene-2-levulinate), MC-A-600 (benzo[ b ]thien-4-yl methylcarbamate), and SD-8447 (2-chloro-1-(2,4,5-trichlorophenyl) vinyl dimethyl phosphate) were effective initially and gave somewhat similar residual control of the 2 species of hornworms.