Technical Abstract: Buffalo fly (Haematobia irritans exigua) and horn fly (Haematobia irritans irritans) cause irritation and production loss in much of the cattle producing area of the world. In Australia losses from buffalo fly were recently estimated at A$78m per year. Control is largely performed by using organophosphate(OP)/carbamate, synthetic pyrethroid(SP) and macrocyclic lactone insecticides formulated for topical use. In Australia resistance to SPs was first recorded in buffalo flies in 1980 associated with oversprays of DDT and fenvalerate. Resistant flies were 45 times less sensitive to fenvalerate than susceptible flies, 29 x less susceptible to cypermethrin and more than 1000 x less susceptible to DDT. By the 1990s resistance to the SPs was widespread in populations from coastal northeastern Australia. Resistance in American horn flies was associated with the kdr and super-kdr point mutations in the gene encoding the voltage gated sodium channel. This study assessed resistance to SPs at the University of Queensland, Pinjarra Hills farm and investigated whether the kdr and super-kdr mutations were present in buffalo fly. The multiplex PCR assay developed to detect the kdr mutations in the horn fly was successful in detecting the kdr mutation in buffalo fly. The super-kdr mutation was not detected in this buffalo fly population.