A field study was carried out in eastern Sudan, near the Ethiopian border, to investigate the abundance, seasonality, man-biting behaviour and resting sites of sandflies in two areas where visceral leishmaniasis (kala-azar) is endemic: Umsalala village, Galabat Province; and the adjacent Dinder National Park (DNP), Dinder Province. Abundance of the different species was determined from collections made, using light and sticky-paper traps, in various habitats between November 1993 and February 1995. Man-biting sandflies were collected as they landed on human bait. The habitats investigated for day-resting sandflies were thatched huts, chicken coops, tree-holes, termite mounds and soil cracks. Animal burrows were not investigated. The species found were Phlebotomus (Larroussius) orientalis, P. (Phlebotomus) papatasi, P. (Paraphlebotomus) saevus, P. (Anaphlebotomus) rodhaini, Sergentomyia (Sintonius) clydei, S. (Sergentomyia) antennata, S. (Sergentomyia) sckwetzi, S. (Parrotomyia) africana and S. (Grassomyia) squamipleuris. Phlebotomus orientalis was the only man-biting sandfly species found in the DNP whereas P. papatasi, P. orientalis and P. saevus were all found in Umsalala. Abundance of each species varied with the habitat. In Umsalala and a camp for game wardens in the DNP, Sergentomyia spp. predominated over Phlebotomus. In the DNP, the most abundant sandfly in a thicket dominated by Acacia seyal trees was P. orientalis, followed by Sergentomyia spp. Significant habitat 'preferences' were observed for most sandfly species in the area. In attempts to find resting flies, P. orientalis was only found resting in the mounds made by the termite Macrotermes herus and P. papatasi was only found inside huts; no resting sites were detected for other Phlebotomus spp. but Sergentomyia spp. were observed in all the sites investigated. The P. orientalis in the DNP showed a clear seasonal variation in abundance, which was closely correlated with the mean monthly temperature and relative humidity of the area. A remarkable increase in the abundance of this vector occurred at the beginning of the rainy season.