Sexual differences in herding behaviour of African buffalo (Syncerus caffer) were studied by analysing at the herd level mitochondrial D-loop hypervariable region I and fourteen autosomal microsatellites. Three herds from Arusha National Park in Tanzania were analysed with mtDNA and five herds from Kruger National Park in South Africa with mtDNA and microsatellites. Significant mtDNA differentiation was observed among herds in Arusha NP (F-ST = 0.12, based on haplotype frequencies). Assignment tests with microsatellite data from Kruger NP showed that most frequent migration between herds is by males greater than or equal totwo years. This was confirmed by tests for herd differentiation and analyses with Lynch and Ritland's relatedness estimator. Within a herd, males younger than two years and females showed a higher relationship through a common father rather than a common mother, indicating that female herd members mate with only a few dominant males. This in turn suggests a female: male sex ratio larger than 5:1. The migration rate per generation between herds was estimated to be 5-20% for females and close to 100% for males. Finally, the implications for the management of buffalo populations are being discussed.