The effect of citric acid conditioning of the root surface in conjunction with gingival flap surgery including barrier membranes (expanded polytetrafluoroethylene) was clinically evaluated in 26 intrabony periodontal defects in 23 patients. Control treatment included gingival flap surgery with barrier membranes alone. Twelve defects were treated with the experimental and 14 with the control protocol. Healing was evaluated 12 months after surgery. Initial probing depths approximated 6.9 mm and defect depths measured during surgery exceeded 4 mm. The patients exhibited good oral hygiene over the study interval as substantiated by low plaque and bleeding scores. Acid conditioning of the root surface did not enhance periodontal healing in this study, similar amounts of defect resolution were observed following either treatment protocol. Probing depth reduction generally approximated 1.8 mm; gain of clinical attachment, 0.8 mm; and defect bone fill, 1.2 mm. Under the prevailing conditions, the barrier membrane procedure apparently gave a healing result beyond which further improvement could not be achieved by root surface conditioning.