This paper reports a paired-groups experimental study, which tests the Interaction Hypothesis in a computer-mediated communicative environment. Pairs of intermediate-level nonnative speakers of English (n = 24) interacted with one another in a synchronous mode over a local area network while attempting to jointly complete jigsaw and decision-making tasks that were seeded with largely unknown target lexical items. The data suggest that learners often engage in negotiated interaction when presented with unknown lexical items during the course of task completion. Results also show that previously unknown lexical items that were negotiated were retained significantly better as measured by immediate and delayed recognition (receptive) and object labeling (productive) posttests than those items where preemptive input alone was provided and where target items were not engaged. The results are interpreted as being supportive for the interactionist perspective on SLA, especially the importance of attention, as they provide evidence of a more direct link between negotiated interaction and acquisition.