Human visceral leishmaniasis (VL) or kala-azar remains a major cause of mortality, particularly in the developing world. The disease is common in the internal regions of north-eastern India, which have a tropical or sub-tropical climate. In a recent study on VL in this region, the relationship between the incidence of VL and certain physio-environmental factors was explored, using a combination of a geographical information system (GIS), satellite imagery and data collected 'on the ground'. Some eco-environmental parameters were then used to map and describe the spatial heterogeneity seen in the transmission of the parasite (Leishmania donovani) that causes VL in India, and to identify those habitats, on the Gangetic plain, where the sandfly vectors might thrive. It was found that the presence of waterbodies, woodland and urban, built-up areas, soil of the fluvisol type, air temperatures of 25.0-27.5 degrees C, relative humidities of 66%-75%, and an annual rainfall of 100-<160 cm were all positively associated with the incidence of VL. A VL map was created and stratified into areas of 'risk' and 'non-risk' for the disease, based on calculations of risk indices.