Previous research suggests that sensitivity to aspects of the self and others develop in tandem. We tested 14- and 18-month-olds' imitative abilities and mirror self-image reactions (i.e., testing behavior and passing the mark test). Results showed that 14-month-olds' imitation was closely related to the occurrence of testing behavior in front of the mirror, where they checked whether they could control the movements of the mirror image. Eighteen-month-olds, however, no longer showed this relation. Furthermore, in 18-month-olds, we found a high association between imitation and passing the mark test. These correlations suggest that infants' mirror self-image reactions and imitation share the ability to detect and produce visual-motor contingencies.