A study explored how writers with extensive experience and learning in an academic discipline used both topical and rhetorical knowledge to construct synthesis essays. Subjects, 20 psychology graduate students and 20 business graduate students, wrote synthesis essays on either the topics of "supply-side economics" or "rehearsal in memory." Half of the subjects completed think-aloud protocols, and their composing processes were analyzed for different qualities and frequencies of elaborations and rhetorical awareness and for task representation. Analysis of variance indicated that (1) "high knowledge" writers evidenced unique elaborative and rhetorically sensitive performance; (2) high knowledge writers included more "new" information in their essays in the top levels of essay organization; (3) low knowledge writers elaborated less but did rely on structural and content-based awareness to compose. Findings confirmed the interrelatedness of comprehension and composing processes and illustrated how writers, with varying levels of topic familiarity, use both their knowledge of disciplinary topics and their experience as readers and writers to compose synthesis essays. (Fifteen tables of data, four figures, and one note are included; 180 references and two appendixes of data are attached.) (RS)