This clinical study compares the diagnostic yield of Kodak Ektaspeed with the diagnostic yield of Kodak Ultraspeed using a split-mouth experimental design and proximal surface carious lesions as the test objects. Assuming that proximal surface carious lesions are distributed randomly in a given patient and in the population at large, then any difference in the diagnostic quality of either of the films should be disclosed as a difference in the frequency and distribution of lesions identified with either of the films. No statistical difference was observed, which suggests that the two films perform equally well for the diagnostic task of detecting proximal surface carious lesions. Considering that there is a 40% to 50% reduction in radiation exposure to the patient when the faster film is used, it appears that Kodak Ektaspeed should be the preferred film for the dental practitioner.