The effect of an interdisciplinary algebra/science course on students' critical thinking skills was examined. A traditional college algebra course was used as a comparison group. The students in the sample enrolled in college algebra and then half were randomly placed into the interdisciplinary course. A quasi-experimental pretest-posttest comparison group design was used. The Watson-Glaser Critical Thinking Appraisal was used to measure the students' critical thinking skills. This instrument consists of an overall critical thinking score as well as five subscores in the areas of Inference, Recognition of Assumptions, Deduction, Interpretation and Evaluation of Arguments. It was found that the students in the interdisciplinary course made greater gains in the overall critical thinking score as well as in four of the five subscores. However, the differences in the gains made in the two courses were not statistically significant. Disregarding course, other factors that were found to be closely related to critical thinking were Composite ACT, grade received in the course, Math ACT and grade point average. It was also found that students whose majors were in the Schools of Arts and Letters or Science and Technology scored higher on critical thinking than students whose majors were in the Schools of Business or Education. Factors found to have no relationship to critical thinking were ethnicity, gender and classification.