The following compounds were tested by knapsack mistblower against the gypsy moth, porthetria dispar (L.): trichlorfon at 4 pounds active per gallon of formulation, SD 8447 (phosphoric acid, 2-chloro-I(2,4,5-trichlorophenyl) vinyl dimethyl ester), and Thuricide® 90TS (Bacillus thuringiensis var. thuringiensis Berliner) containing 30 billion viable spores per gram of liquid. In 3 separate trials each material was tested against 3 different age groups of the larvae. In the 1st trial the larvae were 95% 2nd instar; in the 2nd they were 50% 2nd and 48% 3rd; in the 3rd trial they were 33% 3rd, 61% 4th, and 4% 5th instar, SD 8447 and trichlorfon at 1 pound in 10 gallons of water reduced the larvae on the test apple trees to very low numbers and gave excellent protection of the foliage. In the 2nd trial SD 8447 was used at 0.5 pounds ami also gave full protection. Thuricide 90TS at 10 and 20 pints in 10 gallons of water gave very good protection to foliage and although a few Ian are remained on the tree they apparently did little feeding. Thuricide 90TS at 5 pints per 10 gallons was ineffective and did not prevent complete defoliation.