Transactive memory is the knowledge of what others in a group know and the exchange of that knowledge. In groups with effective transactive memory systems, members know “who knows what”, send knowledge to the appropriate individuals, and develop strategies for retrieving that information (Mohammed & Dumville, 2001; Wegner, 1995). Transactive memory studies tend to focus on the group as a whole, but useful information might be gathered by investigating transactive memory in dyads within groups. The purpose of this research was to use the social relations model (Kenny & LaVoie, 1984) as the basis for operationalizing transactive memory and to examine this new operationalization of transactive memory as it related to group performance. In social relations model terms, an effective transactive memory system was operationalized as consensus about expertise and knowledge seeking. Data were collected from two samples of student engineering project groups (n = 55 groups and n = 77 groups) and a sample of organizational engineering project groups (n = 7 groups). Groups whose members had spent significant time working together were hypothesized to have effective transactive memory systems and to exhibit significant consensus. Groups whose members had spent relatively less time with one another were hypothesized to have poorer transactive memory systems and to make use of unique relations in the group and assimilation as the basis for identifying expertise. The hypotheses were partially supported. In groups whose members spent relatively more time together, there was some agreement about who was expert and from whom to seek knowledge; however, knowledge exchange tended to be mostly based on seeking knowledge from no one or everyone in the group. In addition, group members made use of their unique dyadic relationships with particular others when identifying expertise and seeking knowledge. In fact, members of groups that performed better were likely to exchange knowledge based on their unique dyadic relationships with others. This study advances earlier research on transactive memory by suggesting that dyadic relations within groups are important to fully understanding transactive memory and its relationship with performance