Objective: Subjective and objective measures were used to determine the relative efficacy of 10% and 35% carbamide peroxide gels in bleaching extracted human teeth. Method and Materials: Fifty-five teeth (premolars and molars) were sectioned longitudinally, and one-half of each tooth was assigned to group A (10%) and the other half to group B (35%). Prebleaching shades were evaluated subjectively by 5 experienced observers using standard shade tabs. Photographs were also taken with a calibrated digital camera. Luminosity, R, G, and B levels were determined with Photoshop software. The specimens were then bleached by either 10% or 35% carbamide peroxide, after which they were reexamined by the 5 observers and rephotographed. Results: All bleached specimens were subjectively assessed as "lighter," but there was no perceived difference in final shade between groups. Objective measurement showed that the greatest spread in the 0 to 255 scales was in the B levels. Mean (and range) of pre- and postbleaching B levels and their differences, by group, were group A, 96.2 (76.5 to 117.1), 113.6 (87.7 to 129.1), difference 17.4, and group B, 95.4 (72.1 to 118.8), 110.5 (88.0 to 138.5), difference 15.1. Statistics were performed using paired t tests. These pre- and postbleaching differences were significant (P .002). The difference between mean postbleaching B values was not significant (P = .479). The greatest change in luminosity occurred in initially dark teeth treated with 35% carbamide peroxide (P = .036). Conclusions: Subjective determinations suggest that the bleaching protocols tested were equally effective, but the objective measurements implied that the higher concentration of carbamide peroxide was more effective for darker teeth. Keywords: Adobe Photoshop software, bleaching, carbamide peroxide, discoloration, effectiveness, human observers, value (brightness)