The Polymerase Chain Reaction (PCR), compared to the serological reference technique for the detection of Leptospira spp., was implemented to evaluate its application as a leptospirosis diagnosis method in samples of symptomatic patients of recent infection from the health sector in northwestern México. Samples of 34 patients were analyzed using the PCR and the microagglutination test (MAT). The results obtained by the PCR showed complete concordance with the determinations of positive or indeterminate patients obtained by the MAT. Out of 31 negative samples or not confirmed by the MAT, 7 (20%) were positive by the PCR. The PCR technique implemented in this study showed to be a useful tool in the diagnosis of the leptospirosis combined with the serological test MAT, emphasizing its usefulness for early detection of this disease.