In the present study, we examined two indices of semantic similarity (i.e., latent semantic similarity [LSS], language style matching [LSM]) to determine their respective roles in initial, unstructured dyadic interactions. Transcripts of the dyad members’ conversations were used to compute the LSS and LSM indices, which were then correlated with various dyad-level behaviors and perceptions. The results suggest that LSS develops out of a highly involving interaction between mutually attentive and acknowledging partners in which a lot of verbal information is exchanged. On the other hand, LSM appears to be a behavior that is not associated with interactional involvement per se but may occur when dyad members are in the grip of a strong emotion and tend to repeat each other’s words and phrases in a relatively thoughtless and automatic manner.