This study investigated hydrogen peroxide (H₂O₂) concentration of two home bleaching gels, in their dispensing syringes and their degradation in vivo in intraoral bleaching trays. Two bleaching gels were studied, 7.5% hydrogen peroxide (HP) and 20% carbamide peroxide (CP). The concentration of H₂O₂ was determined in dispensing syringes. Twenty individuals were involved in this study. The gels were placed in trays of both arches and their degradation determined at 5, 10, 15, 20, 30, 40, 60 and 75 min. The concentrations of H₂O₂ in syringes were (HP) 8.12% and (CP) 7.95%. For the HP gel in custom-trays the concentration of H₂O₂ was 73% at 5 min and 42% after 75 min. In the 20% CP gel it was 75% at 5 min and 39% after 75 min. Activity decreased linearly up to 75 min, where the mean concentration of H₂O₂ exceeded 35% for the CP and HP gels.