Objective: To compare the dimensional changes of two autopolymerising denture base resins using three different processing techniques. Method and Materials: Sixty edentulous denture bases were made from the polymethylmethacrylates FuturaGen and PalaXpress. Ten bases were made from each resin using a manual injection technique (MI), a pneumatic injection technique (PI), and the fluid resin technique (F). Posterior palatal gap widths between casts and denture bases were measured. For an additional three-dimensional examination of occlusal changes, 10 maxillary dentures were made using FuturaGen/MI and 10 using PalaXpress/PI. Intermolar widths and changes in vertical dimension were determined. In all groups, measurements were taken after polymerization, after removal and repositioning, after polishing, and after storage in water for 1 and 3 weeks. Data were analyzed by using two-way ANOVA and Tukey test (P .05). Results: There were no differences in dimensional changes of FuturaGen and PalaXpress specimens. The pneumatic injection system produced significantly smaller posterior palatal gaps after storage in water for 3 weeks compared to the manual injection system (P .0005) and the fluid resin technique (P = .003). The posterior gaps of dentures were = 0.04 mm and below the recommended depth for carving a posterior palatal seal (0.4 to 3.0 mm). Conclusion: The processing technique rather than the choice of the two resins seems to be the dominate variable with respect to dimensional changes. Keywords: dentures, dimensional changes, injection system, polymethylmethacrylate, posterior palatal gap, posterior palatal seal