This case study compared the performance of teaching assistants (TAs) who were native speakers and nonnative speakers (NNS) of English during office hour consultations with undergraduates. Three nonnative- and two native-speaking TAs in the economics department of a major American university were videotaped during office hour consultations. The nonnative-speaking TAs were from South America and had scored 200-220 on a language test, corresponding to overall intelligibility but with occasional problems in pronunciation, grammar, and fluency. The videotapes were then analyzed using the conversation analytical approach combined with a broader notion of context and trouble-shooting. The analyses suggested that even though the nonnative-speaking TAs had only an intermediate level of spoken English, language-related trouble in spoken English was rare, and was quickly and effectively resolved within a turn or two. Content-related trouble, however, was more common in the interactions of both nonnative- and native-speaking TAs in the interactions with undergraduates. An appendix provides transcripts of TA-student consultations. (Contains 56 references.) (MDM)