A comparative study among different serovars of Leptospira interrogans was performed in order to prepare antigens to detect IgM antibodies by ELISA in early and late phase of human leptospirosis. Ten serovars were chosen among the most prevalent detected by microscopic seroagglutination (SAM) in São Paulo city. Using ELISA-IgM five of them showed better results (canicola, hebdomadis, icterohaemorrhagiae, cynopteri and brasiliensis). These ones were also studied in a pool. The non-treated antigens showed higher reactivity than the Triton X-100 (4%/50 degrees C/4h). ELISA-IgM using individually or pool of non-treated antigens proved to be reliable with high sensitivity and should be used for an earlier diagnosis of leptospirosis, as a trial test. Faster diagnostic elucidation can be useful to detect epidemic situations, so, allowing epidemiological surveillance interventions.