Scent marking by defecation and urination in numerous small latrines may be related to resource defence in brown brocket deer (Mazama gouazoubira). Both males and females seem to be territorial, and both contribute to latrines where their ranges overlap. Latrines could thus potentially function as centres of information exchange and intrasexual competition. Counter-marking occurs when animals respond to invaders' marks with a greater number of marks. The objectives of this experimental study were to determine whether brown brocket deer distinguish dung of presumed invaders from their own and whether they counter-mark such faecal deposits. Two samples of dung (from unknown males or females and the experimental animal) were introduced near the latrines of 21 captive deer (13 males and eight females), and we observed their responses, including investigative (sniffing) and marking (urination and defecation) behaviours. Males investigated the introduced dung and their own latrine significantly more when the dung was from an unknown male than when it was their own. Females investigated unknown female dung significantly more than their own. Males counter-marked the introduced dung and their latrine significantly more when the dung was from an unknown male than when it was their own. Males marked with a shorter latency and at a greater frequency than females. Our data indicated that males counter-mark most intensively dung from male ‘intruders’ which may be related to intrasexual competition and resource defence. Females showed a non-significant tendency to counter-mark same sex intruders.