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Objective: To determine the efficacy of zeta-cypermethrin in controlling buffalo fly (Haematobia irritans exigua)., Design: Five field trials in northern and central Queensland., Procedure: Zeta-cypermethrin pour-on at 2.5 mg/kg, spray at 62.5 ppm, deltamethrin pour-on and pour-on vehicle were applied to groups of 20 cattle. Buffalo fly counts were conducted three times before treatment and 3, 7, 14, 21, 28 and 35 days after treatment., Results: In central Queensland where synthetic pyrethroid resistance in buffalo fly populations was rare, 2.5 mg/kg of zeta-cypermethrin pour-on gave good control of buffalo fly for 4 weeks and was better than a deltamethrin product. A zeta-cypermethrin spray used at 62.5 ppm gave 14 days control. In far-north Queensland where resistance to synthetic pyrethroids and heavy rain was common, the maximum period of efficacy of zeta-cypermethrin pour-on was reduced to 2 weeks., Conclusion: In areas where there is low resistance to synthetic pyrethroids among buffalo flies, zeta-cypermethrin pour-on can be expected to give good control for 4 weeks.