The 1993 Illinois Goal Assessment Program (IGAP) Reading Tests measured reading comprehension using both narrative and expository reading passages. Noticeable differences in mean scaled scores occurred depending on whether the 1993 results were equated back to the 1992 narrative test or the 1993 expository test (Hsu and Ackerman, 1994). In an attempt to explain these disparate results, this investigation examines whether combining the two types of passages on a reading test induces multidimensionality. The tests were administered to all Illinois students in grades 3, 6, 8, and 10, and tests from nearly 5,000 examinees were used in the analysis. Results from a principal components factor analysis, a statistical test of dimensionality, and multidimensional item-response theory suggest that items based on the narrative and expository passages measure distinct, yet highly correlated, dimensions. Four figures and five tables present study findings. (Contains 14 references.) (Author/SLD)