The main endemic area of kala-azar (visceral leishmaniasis) in the Sudan is in Eastern State and the Blue Nile area of Central State. In order to obtain more recent information about kala-azar in both States, the major hospitals and health centres were visited, the physicians and medical assistants interviewed and available records inspected. In Eastern State a cross-sectional survey of one village was carried out and a longitudinal population-based study of another village started. In this State, after a decline since 1985, a sharp increase in the number of cases was noted from 1991 onwards. This increase was seen in large areas, especially along the Rahad and Dinder Rivers. In contrast, in Central State, there was a decline in the frequency of the disease since the 1960s in the area around Sennar and Singa, which was regarded as a hyperendemic focus up to about 30 years ago. It was hypothesized that this decline may be related to the extensive agricultural development with regular insecticiding and the deforestation of the area. Several aspects with regard to transmission of kala-azar are discussed.