A dot-ELISA was evaluated using antigen obtained from Leptospira interrogans cultures of the serovars brasiliensis, canicola, cynopteri, hebdomadis, and icterohaemorrhagiae for the detection of human IgM, IgG, and IgA. Single serum samples from 63 patients with the icterohemorrhagic form of leptospirosis in the acute phase, collected 3-14 days (mean = 7 days) after the onset of symptoms were tested. Ten patients were examined during convalescence and followed up for a period of 4-12 months. For a control group, serum samples from 10 apparently healthy individuals with no clinical or epidemiologic history of leptospirosis, and from 38 patients with nonleptospiral illnesses were used. In the acute phase, IgM antibodies were detected in 62 (98%) of 63 patients and IgG and IgA were observed in 70% and 76% of them, respectively. For the admission serum samples, the predictive value negative of the dot-ELISA was 98% for IgM, 72% for IgG, and 76% for IgA detection. All 10 patients followed-up during convalescence showed IgM antibodies up to the sixth month, decreasing to 57% by the 10th month, and persisting in only one of six patients during the 11th and 12th months of follow-up. Immunoglobulin G was detected in six patients up to the fourth month and in two of six individuals up to the end of follow-up. Immunoglobulin A was observed in all patients up to the end of the first month, decreasing progressively up to the sixth month, and was no longer detected in any patients from seventh to the 12th months of follow-up. The dot-ELISA can be used as an important laboratory screening test, especially when detecting IgM antibodies. It proved to be effective in the diagnosis of human leptospirosis, and appears to have advantages in terms of yield, time, and case of execution and low cost.