In mammals, which are territorial only during the breeding season, territoriality is mainly controlled by androgens, including testosterone. Dehydroepiandrosterone (DHEA) is supposed to be the key hormone that regulates mammalian territoriality outside of the breeding season. The aim of this study was to determine whether DHEA affects territorial behaviour of male American martens (Martes americana) during the non-breeding season. Therefore, we studied levels of DHEA and testosterone and spacing behaviour of male American martens (n = 40) on Chichagof Island (1113 km2, 57-58°N, 135-136°E, Alaska, USA) from September to June. Using the capture-recapture and radiotelemetry methods, we distinguished between resident (n = 33) and transient (n = 7) males. The levels of hormones were assessed from their blood plasma. We predicted: (1) higher levels of DHEA and testosterone in resident than in transient males; (2) higher levels of DHEA and testosterone in younger than in older males; and (3) higher levels of testosterone, but not DHEA, before than after the breeding period. In accordance with our prediction, resident males had higher testosterone levels than transient males (p < 0.001). However, resident and transient males did not differ in their DHEA levels (p = 0.69). Younger residents had higher DHEA levels than older residents (p = 0.02). On the other hand, testosterone levels did not change with age of the male (p = 0.81). As we predicted, marten males had higher testosterone levels before than after the breeding period (p < 0.001); but their DHEA levels did not change with seasons (p = 0.58). Our results indicate: (1) male martens might acquire their own territories owing to higher levels of DHEA; (2) resident males could successfully defend their territories during the breeding season due to higher levels of testosterone.