Due to the high olfaction acuity of dogs, they are used to detect the cryptic or hidden objects like explosives and narcotics. The current study was conducted to evaluate the impact of dog breeds, searching site and previous training experiences on the dogs’ detection performance for narcotics. One hundred and sixty-five purebred dogs from four breeds, German shepherd (n=46), Labrador retriever (n=41), Belgin malinois (n=40), and Rotweiller (n=38) were utilized. Dogs have examined shortly before the first certificate for the operational efficiency, during police certification exams and also, during an annual recertification exam assuring proficiency. The obtained results demonstrated that Labrador retriever was the highest in correct alert and the lowest in false alert, miss trails, and passes without indication. Dogs performed better during first police exams for certification than during the final stage of training and annual recertification. A significantly higher proportion of correct alert and a lower false alert were recorded inside the cars in comparison to other searching sites. Conclusively, Labrador retriever breed was the superior breed in narcotics detection and were easily found inside cars, while and best detection performance was for dogs during first police certification exams.