In mating systems that involve competing males and choosy females, males are expected to advertise their genetic quality to discriminating females. Most examples have focused on visual or acoustic signals, such as ornamentation or song; yet arguably, olfactory communication may be more important to the majority of vertebrates with the possible exception of birds. Fortunately, attention has begun to shift to the role of odours in mate choice, with most of that attention being directed at the major histocompatibility complex or more recently at the major urinary proteins. The study of male ring-tailed lemurs presented by Charpentier and colleagues in this issue adds a new dimension to investigations of the influence of genes on mate choice via odour production. By comparing genetic heterozygosity to the production of semiochemicals in the scrotal scent gland, they provide a link between genetic composition and scent-marking behaviour as a potential advertisement of male quality.