This study investigated the effects of argument scaffolding and source credibility on science text comprehension. Eighty-seven college students were randomly assigned to an argument scaffolding activity, or no scaffolding, and read 2 science texts, attributed to a high- or a low-credibility source. The argument-scaffolding group recalled less text-based information but generated more knowledge-based inferences than did the no-scaffolding group. High source credibility enhanced readers' text-based recall but had little effect on knowledge-based inferences or situation models. Overall, results suggest that argumentation facilitates deeper text comprehension and better argument understanding, while at the same time reducing the effect of source credibility on text processing.