A series of three studies examined the influence of prior knowledge on expert readers' main idea construction processes. Eight expert readers read texts from familiar and unfamiliar content domains, and gave verbal reports of the processes they used for constructing main ideas. Five distinct main idea construction processes were reported: (1) initial hypothesis, (2) topic/comment, (3) draft and revise, (4) listing, and (5) automatic main idea construction. A significant interaction was found between main idea construction process type and text familiarity. Results indicated that the relative familiarity of the text topic influences the type of main idea construction process used. The think aloud protocols also allowed examination of the processes used in concert with main idea construction, including importance assignment, hypothesis testing, and comprehension monitoring. The findings imply that teachers should acknowledge the difficulty of the main idea extraction process and model the process for their students. (Three appendixes contain descriptions of texts used in the experiments, instructions given to subjects, and a description of the verbal transcription method. Two pages of references are included.) (SKC)