The benefits of synergistic collaboration are at the heart of arguments in favor of pair programming. However, empirical studies usually investigate direct effects of various factors on pair programming performance without looking into the details of collaboration. This paper reports from an empirical study that (1) investigated the nature of pair programming collaboration, and (2) subsequently investigated postulated effects of personality on pair programming collaboration. Audio recordings of 44 professional programmer pairs were categorized according to a taxonomy of collaboration. We then measured postulated relationships between the collab- oration categories and the personality of the individuals in the pairs. We found evidence that personality generally af- fects the type of collaboration that occurs in pairs, and that different levels of a given personality trait between two pair members increases the amount of communication-intensive collaboration exhibited by a pair.