The determinants of male reproductive success in primates are widely studied in species with male dominance. However, studies on species where females seem to have much power and are able to choose their mating partner are rare. To comprehend the social system of a female dominated species, it is important to understand the factors that influence male reproductive success. I intend to determine male reproductive success of the vervet monkey, Chlorocebus aethiops pygerythrus, a species with powerful females. In the Samara Private Game Reserve, South Africa, I will collect blood and faecal samples from mother-infant pairs and all potential sires to test paternity. These data will be complemented by individual life history data and observational data to determine which factors influence male access to fertile females.