Government-owned Hereford and Angus yearlings on pasture at Camp Stanley and Camp Bullis, Bexar County, Texas, that are naturally infested with the common cattle grub, Hypoderma lineatum (de Villers), are treated with new animal systemic insecticides detected with the mouse-Cuterebra animal systemic insecticide test (Drummond, R.O., 1979, Insect. Acaric. Tests 4:216-7). Animals are weighed and given insecticides in initial tests either orally by capsule (usually technical grade insecticide) or dermally by whole-body spray of 4 litres/animal at>150 psi (usually formulated as an EC in xylene (65 parts), Triton X-100 (10 parts), and Al (25 parts). In other tests, insecticides may be administered dermally by pouron of a specific volume of insecticide (usually water-diluted EC as above or solution in oil) per body weight or intramuscularly by injection (usually technical grade insecticide in diethyl succinate). Normally, cattle are treated initially at the highest nonlethal dosages as determined by cooperating veterinary toxicologists; maximum dosages of initial tests are 100 mg/kg orally and 1% spray. After the treatment in May or June, the backs of treated cattle (usually 3 animals/treatment) and untreated cattle of the same age and breed from the same herd are examined monthly from August to Feb. of the next year for encapsulated cattle grubs. As cattle grubs appear, they are located on an outline map of the back of each animal; the cumulative number of grubs in each animal is obtained. Effectiveness of a treatment is determined by comparing the average number of grubs in treated cattle with the average number In untreated cattle. The most recent report of tests with new systemlcs in cattle was presented by Drummond, R.O., 1979, Insect. Acaric. Test 4:209.