A dipstick assay for the detection of Leptospira-specific immunoglobulin M (IgM) antibodies in human sera was evaluated in 27 laboratories in 23 countries. 873 serum samples from 711 patients including 329 laboratory-confirmed leptospirosis case patients, 239 noncase patients and 69 patients with viral infections causing heamorrhagic fever were tested. Relative to the results of the reference leptospirosis test, the sensitivity of the dipstick assay was 84.5% for serum samples collected during the first 10 days of the disease and 92.1% for serum samples collected 10-30 days after the onset of disease. The specificity was 87.5% and 94.4%, respectively. Similar to viral haemorrhagic fevers, leptospirosis may cause bleeding. A small number of serum samples from patients with haemorrhagic viral infections gave a weak (1 +) stain. All other samples were negative. In conclusion, the dipstick assay is sensitive and specific and reacts well with serum samples from patients infected with a range of leptospiral strains. It is also easy to use and does not require special equipment or refrigeration. Therefore the assay is ideal for use in developing countries and rural settings.