A study explored similarities and differences in relative pronoun use by native speakers (NSs) and non-native speakers (NNSs) of English. The study was conducted with 40 university students, 20 NSs and 20 NNSs. Specifically, the study examined the frequency of relative pronoun use and the spontaneity of subjects' responses in completing a sentence combining task. It was found that: (1) more NNSs used relative pronouns than NSs, (2) more beginning-level NNSs used relative pronouns than advanced-level NNSs, and (3) more NSs were aware of the contextual variability of the structure of the complex sentence than NNSs. Findings suggest that frequency of relative pronoun use characterizes the current developmental stage of the learner's interlanguage system, and that the awareness of stylistic/contextual differences in sentence structures distinguishes NS competency from less advanced interlanguage competency. Contains 10 references. (Author/MSE)