An examination was conducted of the planned and unplanned speech of 24 native speakers of Mandarin and Korean who were serving as teaching assistants at the University of Illinois at Chicago. Each was videotaped on two occasions two weeks apart in a preparation course for international teaching assistants (ITAs), in which instruction in the use of discourse markers was a major focus. On the first occasion, the subjects pre-selected a concept or specific problem anticipated in an introductory course and prepared a presentation on it. On the second occasion, the subjects were given a list of 10 topics and had 3 minutes in which to prepare a presentation on one of them. For comparison, the responses of five native-English-speaking teaching assistants to questions posed to them were examined. Discourse features examined in all instances included definition, example/illustration, restatement/rephrasing, identification/naming, introduction/new topics, and summary/review. The ITAs' planned discourse was found to contain more elaborate marking and more of it, than the unplanned discourse. Native speakers did not do more marking than ITAs, contrary to expectation. However, raters understood the native speakers more easily, suggesting native speakers have other ways of making discourse comprehensible. A 32-item bibliography is included. (MSE)