This study explored the relationship between discourse topics and interlanguage variation, describing the following: relationships between discourse topics and a second language learner's participation in native speaker/non-native speaker (NS-NNS) conversation; relationships between discourse topics and the grammatical complexity, accuracy, and fluency of a second language learner's oral production; and how second language acquisition processes such as language transfer would occur differentially within discourse domains. Data were collected through one Taiwanese graduate student's conversational interactions over time with an English NS and a Japanese graduate student who met regularly to practice English. Six NS-NNS conversation topics were covered. Data were analyzed for dominance, syntactic complexity, accuracy, and fluency. In a second study, six Taiwanese in the United States listed discourse topics they would like to discuss and topics they felt neutral about. Each participant gave a presentation on their topic of choice and completed an interview about their process of selecting and presenting a topic. Transcripts were analyzed for grammatical complexity, fluency, and accuracy. Overall, results indicated that discourse topics affected second language learners' conversational participation. Willingness to participate in a conversation depended upon familiarity with the topic. (Contains 18 tables and 26 references.) (SM)