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This study was aimed to determine the effects of μ- and κ-opioid receptor activation in relation to the social status of mice, being a winner with repeated experience of victories or a loser with repeated experience of social defeats. The behaviors of the animals were assessed in a social encounter test measuring the communicative behavior towards a familiar and an unfamiliar partner behind a perforated transparent partition (partition test) and in an elevated plus-maze test estimating the anxiety level of mice. Placebo and graded doses of the μ-opioid receptor agonist DAMGO (0.5 and 2mg/kg s.c.) and the κ-opioid receptor agonist U-50,488H (0.6, 1.25, and 2.5mg/kg s.c.) were administered to the control mice, winners and losers in two experiments. In the partition test, the winners spent somewhat more time and the losers less time than the controls in the vicinity of their partner probably related to a lower and higher …