Pyrethroid insecticides combine a high efficacy against insects with a low toxicity towards warm-blooded vertebrates. For this reason they are largely used to control housefly infestations. The efficacy of these products is affected by insecticide resistance mechanisms. In particular, some mutations in the sodium channel coding sequence are responsible for target-site resistance to pyrethroid insecticides. This work presents a new molecular approach based on allele-specific PCRs to point out and to characterise this resistance mechanism in two M. domestica populations (PNT and TRV) collected near Piacenza (Northern Italy). The presence of different kdr and s-kdr genotypes was assessed for population PNT whilst kdr only was detected in population TRV. Dose-response bioassays evidenced quite high resistance factors, expecially for population PNT. This is in line with the kdr and s-kdr frequencies observed in the assayed populations.