Naked mole-rat colonies exhibit a high reproductive skew,breeding being typically restricted to one female (the 'queen') and one to three males. Other colony members are reproductively suppressed, although this suppression can be reversed followingthe removal or death of the queen. We examined dominance andqueen succession within captive colonies to investigate the relationship between urinary testosterone and cortisol, dominance rank and reproductive status; and to determine if behavioural and/or physiological parameters can be used aspredictors of queen succession. Social structure was characterized by a linear dominance hierarchy before and after queen removal. Prior to queen removal: dominance rank was negatively correlated with body weight and urinary testosteroneand cortisol titres in males and females. Queen removal results in social instability and aggression between high rankingindividuals. Dominance rank appears to be a good predictor of reproductive status: queens are the highest ranking colony females and are succeeded by the next highest ranking females.The intense dominance-related aggression that accompanies reproductive succession in naked mole-rats provides empirical support for optimal skew theory.