This study used concept maps to investigate the effect of using graphing calculators on students' understanding of the derivative at a point. The study looked for differences between the concept images that are held by students' who are using graphing calculators and the students who are not using them. Seventy one students enrolled in two different first semester calculus classes at two universities participated in the study. Participants drew concept maps for the derivative. Analysis of the maps showed that students' in the experimental class showed more representations of the concept of the derivative at a point in their maps than the ones in the traditional class. This implies that the experimental group's concept image of the derivative at a point is richer than that of the traditional group. (Contains 2 tables and 5 figures.)