Abstract: A systemic insect repellent composition is provided which affords essentially continuous protection of domesticated animals against fleas, ticks and other blood feeding pests. The systemic compositions of the invention comprise two essential ingredients: Vitamin B.sub.1 and allyl sulfide (garlic oil) dissolved in a soybean oil base. The composition is preferably consumed by the animal during its normal feeding. The dosage consumed by the animal is adjusted to provide a prescribed minimal blood level which insures continuous insect repellency. Unlike the more popular preparations, this composition is not inherently toxic, is not offensive to the animal and does not give the animal bad breath.