The microscopic agglutination test as well as polymerase chain reaction on blood, urine or organs are available for practitioners to diagnose canine leptospirosis. The microscopic agglutination test is still the reference test despite some known pitfalls (delayed serologic response with frequent negative titers in the first week of illness, vaccinal titers confusing interpretation of serologic results, possibility of titers resulting from previous exposure to pathogenic strains). The polymerase chain reaction could be helpful in the diagnosis, especially in the first week of illness or with recent vaccinal history. However some dogs can be asymptomatic carriers and shed leptospires in their urines. Moreover, there is currently limited information regarding the validity of polymerase chain reaction assays for detection of leptospirosis in dogs. As positive titers can be encountered in apparently healthy dogs and as asymptomatic shedding does exist in dogs, laboratory results must always be cautiously interpreted in conjunction with clinical picture. Currently, the microscopic agglutination test and the polymerase chain reaction appear to be complementary. They should be done concurrently and interpreted together in a specific medical context.