 Background: Platelet-rich fibrin PRF is a second-generation platelet concentrate which releases various growth factors that promote tissue regeneration. Metformin MF, a member of biguanide group has been shown to facilitate osteoblast differentiation and thus may exhibit a favourable effect on alveolar bone . Current study was designed to evaluate the combined efficacy of PRF and 1 MF gel with open flap debridement OFD in treatment of intrabony defects in chronic periodontitis CP subjects. 