One zebu bull of 365 kg live weight was treated along the back line with 36 mL of fipronil as a pour-on formulation. Long-lasting mortalities of Glossina palpalis gambiensis were recorded despite exposure to sunlight and regular rinsing with 50 L of water during the following 5 months. Significantly higher mortalities were still observed even 140, 170 and 190 days after treatment following their triple releases or triple feeding of caged tsetse on the treated bull. Mortalities of 70, 80 and 44 %, respectively, were recorded after 15 days of observation. This contrasted with the mortalities of control flies that were released in the presence of the untreated bull or fed in cages on the animal, amounting to 20 and twice 10 % after 170 and 190 days. The feeding successes of the released or caged flies were higher than 95 % and did not differ between control and experimental groups, indicating no repulsive or irritant effects of fipronil. The findings of this study are discussed, particularly in view of the potential of fipronil as an effective means for tsetse control.