The mating system and ecology of black lechwe Kobus leche smithemani was studied in the Bangweulu Basin, northern Zambia. Black lechwe were migratory and concentrated at high density during the wet season on shallow water floodplain and peripheral grassland. Female lechwe were evenly distributed in small groups within the two major habitat types, and density was related to water depth and the quality of vegetation. A proportion of the adult male population defended small, contiguous, resource-based territories of approximately 1–2 ha in size. Particularly high density concentrations of male and female lechwe occurred on small raised areas, which remained dry in comparison to the inundated floodplain. These areas superficially resembled the leks of other reduncine antelope. However, the presence of vegetational resources and the comparatively low levels of agonistic and sexual behaviour suggested that raised areas were clusters of resource-based territories. We suggest that the absence of lek-breeding in this high density population of lechwe is related to the homogeneity of vegetational resources and the corresponding even distribution of females. This may have led to a reduction in male harassment of oestrous females and the increased ability of males to retain oestrous females within single resource territories.