Marked, released horn flies, Haematobia irritans (L.), were resighted on surrounding herds of cattle to determine flight potentials. Horn flies were quickly resighted up to 5 km away. Intervening woodlands and winds did not prevent long flights. Most marked horn flies were released >1 km from any cattle to ensure long-range host seeking. When released close (0.1–0.5 km) to cattle, most marked, resighted horn flies were on the nearby cattle, but even then some horn flies made flights of up to 5 km. These findings support the earlier conclusion that immigrating pyrethroid-resistant horn flies can introduce resistance into an untreated, susceptible population. In areas where resistance occurs, the presence of these immigrating resistant individuals must be considered to plan effective resistance management.