This study analyses intermediate and advanced learner-learner and learner-native speaker (NS) interaction looking for collaborative dialogue. It investigates how the presence of a NS interlocutor affects the frequency and nature of lexical language-related episodes (LREs) spontaneously generated during task-based interaction. Twenty-four learners of English as a foreign language and eight English NSs participated in the study. The results obtained confirm that lexical LREs tend to be more frequent and more likely to be successfully resolved in learner-NS than in learner-learner interaction. However, the analysis of the patterns of interaction of two selected dyads reveals that not all NSs can be expected to provide the same kind of linguistic assistance to the learner. The participants' collaborative or non-collaborative orientation to the activity, shaped by their goals and level of involvement in the task, seems to have a stronger effect on the nature of the interaction and the opportunities this offers for LREs and learning than the overall proficiency of the dyad.