Leptospira, the causative agent of leptospirosis, is a highly invasive spirochete that efficiently colonizes target organs after penetrating the host. Serovar diversity among pathogenic leptospires has been attributed to differences in the structure and composition of lipopolysaccharide (LPS). Leptospiral LPS can elicit protective immunity but is serovar specific. Given the difficulties in preparing multivalent LPS vaccines, the identification of conserved protein antigens for vaccine development is being pursued. Four predicted coding sequences (LIC12880, LIC10793, LIC12892 and LIC12906) selected from the genome of L. interrogans serovar Copenhageni were cloned, proteins expressed and purified by metal affinity chromatography. These proteins have lipobox sequence tag at the N-terminus and are probably new surface lipoproteins. The structural integrity of the purified proteins was assessed by CD spectroscopy, which revealed alpha-helices for LIC10793 and LIC12892 and beta-sheet for LIC12880 and LIC12906, as predominant molecule populations. The reactivity of these proteins with antibodies present in serum samples from patients diagnosed with leptospirosis was evaluated by western blot and ELISA. Our results showed that LIC12880, LIC10793 and LIC12892 were recognized by antibodies in human serum from patients in the covalescent phase of the disease; two proteins LIC10793 and LIC12892 were also reactive with antibodies present in the initial phase of the disease while LIC12906 showed no reactivity. At present, diagnostic of leptospirosis is performed by MAT (micro agglutination test) which detects anti-LPS antibodies in patient's serum only ca. two weeks after the infection. Although preliminary, our results suggest that proteins LIC10793 and LIC12892 are good candidates for development of the much needed diagnostic kit for detection of the disease in its early phase. To our knowledge, this is first report of leptospiral proteins capable to give positive results at the beginning of human infection, when MAT is still negative, and deserves a thoroughly investigation.