Objectives: This double-blind study examined the bleaching effectiveness of two 30% carbamide peroxide bleaching gels: one with 5% potassium nitrate (treatment A) and one without (treatment B). The treatment time was reduced for this pilot study to one hour per day for 10 days to determine whether the higher concentration would whiten teeth and to ascertain the tooth sensitivity and gingival effects of the 30% solution. Method and Materials: Forty subjects were selected with an initial tooth shade corresponding to Bioform shade guide B65 or darker. After obtaining consent, subjects were randomly divided into two groups (n = 20). Custom-fabricated bleaching trays were made for each subject. Trays did not extend onto the gingiva. Each subject was instructed in the placement and wear of the tray and bleach and supplied with one of the two bleaching gels. Subjects had 10 hours of treatment time with the bleaching gel. Photographs and shades (using a standardized Bioform shade guide) were taken at baseline and at final recall to determine bleaching effectiveness. Tooth sensitivity was measured at baseline and final recall by applying a pellet saturated with skin refrigerant to the tooth for 2 seconds. The sensitivity was recorded on a scale ranging from 1 to 10. Gingival index was also measured at baseline and at final recall. Data was analyzed with Wilcoxon rank-sum and Wilcoxon signed rank tests. Results: No significant differences were found for changes in color, tooth sensitivity, and gingival condition between the two bleaching gels (P = .899, P = .375, and P = .056, respectively). Within each group, bleaching gel A and B significantly whitened teeth (P .0001 for both groups). There were no significant changes in tooth sensitivity and gingival condition for gel A (P = .057 and .063, respectively) or gel B (P = .911 and .510, respectively). Conclusion: Thirty percent carbamide bleaching gels effectively whiten teeth without causing a significant increase in tooth sensitivity or changes in gingival condition. Potassium nitrate has little effect in sensitivity when treatment time is short. Schlagwörter: carbamide peroxide, gingiva, potassium nitrate, tooth sensitivity, tooth whitening