Effectiveness of insecticides and application methods was evaluated by ability to eradicate sheep ked, Melophagus ovinus (L.), and sheep biting louse, Bovicola ovis (L.), from farm flocks, criterion being absence for at least 1 year following treatment. Sheep ked eradication was achieved by high-pressure sprays of 1-1½ gallons per sheep of 0.25% DDT or malathion; 0.1% dieldrin, ronnel, or coumaphos; 0.03% diazinon, and 0.015% diazinon. Sheep ked eradication was achieved by ordinary garden sprinkler-can application of 0.5% ronnel (1.3 pints per sheep) , 0.25% ronnel (1.0 to 2.0 pints) , 0.1% ronnel (2.4 pints) , 0.06% diazinon (0.7 to 1.3 pints) , and 0.03% diazinon (0.9 to 2.0 pints). Low-volume spraying was similarly effective using 0.03% or 0.06% diazinon at as low as 0.8 pints per sheep, 0.25% ronnel (1.5 pints), or 0.1% dieldrin (2.3 to 3.5 pints). 0.5% DDT, 2.6 to 3.4 pints per sheep, did not eradicate keds. Only 0.5% DDT high-volume spray (1 gallon per sheep) and 0.5% ronnel sprinkler-can treatment (1 quart per sheep) resulted in eradication of sheep biting lice in all flocks treated. 0.03% and 0.06% diazinon low-volume spray or sprinkle eradicated lice from 4 of 8 flocks treated.