Causes, consequences and pheromonal regulation of male contest and female choice in the staphylinid beetle, Aleochara curtula (Goeze), have been investigated in the field and in the laboratory. At the feeding and mating site (carcass) the sex ratio is male biased. Polyandry is affected by prolonged copulations, spermatophore plugs and anti-aphrodisiac pheromones transferred from the male, and by female repulse behaviour as well. Aggression of competing males leads to expulsion of inferior males from the carcass. Young, starved and multiply mated males, which need access to the food resource, produce the female sex pheromone. They release homosexual responses, but also avoid intrasexual aggression. On the other hand, females behave aggressively towards individuals bearing the female sex pheromone or repulse their copulatory attempts. Those males of insufficient physiological condition produce a lighter spermatophore and fertilize less eggs. The adaptive significance of female mimicry, male mating tactics, and female choice is discussed.