This study tested a refined version of the discourse domain hypothesis, which defines the discourse domain as a topic area in which second language learners demonstrate extensive, current, and important knowledge, including both cognitive and affective dimensions. The study tested the results of previous studies, which showed that learners show enhanced performance on discourse domain topics. Subjects were eight learners of English as a Second Language (ESL) in an intensive college-level ESL program. Four (invested subjects) were interviewed on major field and neutral topics, and four (uninvested subjects) were interviewed on two neutral topics. Students' discourse was analyzed for fluency, syntactic development, and discourse organization. Results indicated enhanced performance by one invested subject on all three measures on the major field topics. The remaining three invested subjects produced ambiguous results, whereas the control group showed little variation across topics. It is concluded that the study provides a measure of support for the discourse domain hypothesis, and lays the foundation for further research in the area of topic-related language use variation. Contains 17 references. (Author/MSE)