Recently, a number of scholars have presented compelling analyses of rhetorical stategies that are employed in scientific texts. What has not been studied in as much depth are issues of whether and how the scientific readers of the discouse respond to such rhetorical cues and how much influence these cues have on the reading process--including what they choose to read and how they allocate their time between comprehension and evaluation. In this study, I begin to address these issues by examining scientists reading and reacting to a single scientific text, Stephen J. Gould and R. C. Lewontin's "The Spandrels of San Marco and the Panglossian Paradigm: A Critique of the Adaptationist Programme." This article, which contributed to a still current and heated debate in evolutionary biology, employs both standard scientific arguments and some that depart quite radically from normal "objective" scientific style. Reading-aloud protocols and interviews were collected from professors and graduate students in evolutionary biology. Overall, comments from both groups clustered at specific points in the text, revealing sophisticated engagement with the authors' arguments. Gould and Lewontin's arguments, and their attempts to guide scientists to read their article in particular ways, did not entirely succeed but the article did provoke productive response. The graduate students and professors exhibited quite different reading strategies, pointing to a long-term process of learning how to read in a profession.