The effectiveness of two pyrethroids, fenvalerate and deltamethrin, against the fly Haematobia irritans exigua de Meijere (Diptera: Muscidae) on buffalo was considered in a field trial. Fenvalerate provided 100% control for 1, 2 and 4 weeks at concentrations of 0.03, 0.04 and 0.05%, respectively. Concentrations of 0.01 and 0.02% were less effective. One hundred percent control of this fly was obtained with deltamethrin for 2, 3 and 6 weeks at concentrations of 0.003, 0.004 and 0.005%, respectively. Deltamethrin concentrations of 0.001% and 0.002% achieved fly control for only 1-2 weeks, respectively.