A potential determinant of peoples selective attention is offered by the structural-alignment view of comparison. This view holds that objects are compared via structured representations that align sets of features that share relational roles. A central claim of this account is that the comparison process directs attention towards alignable features. This prediction has been supported by offline measures by Markman and Gentner (1997), who showed that alignable features serve as better cues for recall than nonalignable features. The present study provides the first online test of the structure-alignment theorys claim that alignability drives selective attention. Consistent with this, we show that in addition to serving as better cues for recall, alignable differences are attended more than nonalignable differences. Within-trial attention dynamics revealed that attention to alignable differences¬¬¬¬ increases over the course of the comparison process.