This article investigates the effects of graduate science students' domain-specific knowledge and language proficiency on local lexical and syntactic processing and on semantic and higher conceptual processing of biology texts written in the students' first and second language. In our research, language proficiency consistently affected lower-level processing. However, it appeared to have few concomitant effects on processing of semantic information. Domain-specific knowledge, on the other hand, affected every aspect of comprehension of semantic information that was assessed in the study. However, it had fewer effects on local lexical and syntactic processing. These results were consistent with theories of discourse comprehension that view processing of local lexical and syntactic information and processing of semantic and higher conceptual information as being both multilevel and modular. The results of the study also suggest that caution should be exercised when applying conclusions drawn from studies of languages from the Indo-European family to languages of a greater linguistic distance, such as Chinese.