Results are reported for 13 systemically active insecticides used in screening tests and in initial practical tests against cattle grubs ( Hypoderma spp.). Results of additional tests against cattle grubs with eight compounds about which preliminary data were reported in 1960 or 1962 also are presented. Treatments highly effective against cattle grubs were: American Cyanamid CL-38023, O,O -dimethyl o-p -(dimethylsulfamoyl)phenyl phosphorothioate, 10 mg./kg./day for 10 days in feed or 20 mg./kg. intramuscular injection; Bayer 29493, O,O -dimethyl O -[4-(methylthio)- m -tolyl] phosphorothioate, 2.5 mg./kg./day for 10 days in feed or 5 mg./kg. intramuscular injection; Bayer 37341, O,O -diethyl 0-4-(methylthio)-3,5-xylyl phosphorothioate, 10 and 50 mg./kg. drench, 5 mg./kg./day for 10 days in feed, or pour-on of 250ml. of 2% in water; Bayer 37342, O,O -dimethyl O -4-(methylthio)-3,5-xylyl phosphorothioate, 10 mg./kg./day for 6 days in feed, 15 mg./kg. intramuscular injection, or pour-on of 125ml. of 2% in oil or water; butonate, 5 or 10 mg./kg./day for 10 days in feed; Rhodia RP-9895, O,O -dimethyl S -(2-[(1-methylearbamoylethyl)thio]ethyl) phosphorodithioate, 15 mg./ kg./day for 10 days in feed; Stauffer R-1504, O,O -dimethyl S -phthalimidomethyl phosphorodithioate, 2.5 mg./kg./day for 10 days in feed, 0.5% spray, or pour-on of 250 ml. of 2% in oil; Stauffer R-3352, S -diphenylmethyl O,O -diethyl phosphorodithioate, 25 mg./kg. by capsule; and Stauffer R-3828, S -(pchlorophenyl) phenylmethyl O,O -diethyl phosphorodithioate, 100 mg./kg. by capsule.