Two experiments investigated predictions from social identity theory and relative deprivation theory regarding membership in low-status groups, using a 3 (legitimacy of low status) X 2 (permeability of group boundaries) X 2 (stability of group status) between-subjects design. Main dependent variables concerned in-group identification and individual and collective mobility attempts. Group members considered their low status more acceptable when it seemed legitimate. In Experiment 1 (N = 184), illegitimate assignment of low status to the Ss' group increased in-group identification. In Experiment 2 (N = 178), illegitimate allocation of individual Ss to a low-status group decreased group identification. Attempts to acquire higher status individually (individual mobility) or collectively (group mobility) were more strongly affected by prospects for status improvement than by legitimacy manipulations.