The purposes of the present study were to examine the frequency of cervical enamel projection in mandibular molars w ith class II furcation defects and to examine the response of these teeth to guided tissue regeneration procedures. Probing depth and vertical and horizontal peridodontal attachment levels were recorded with a constant-force electronic periodontal probe. Following surgical exposure of the bifurcation and prior to membrane placement, the cervical enamel projection was examined and then graded clinically; photographs were taken to allow further examination of the bifurcation. An overall improvement in clinical parameters was observed in most sites. Cervical enamel projection was present in 82.1% of all molars examined. Grade II was the most prevalent (34.8%). Patients with any degree of cervical enamel projection demonstrated significantly higher mean probing depths at baseline than did patients without cervical enamel projection. Likewise, pretreatment probing attachment levels were higher in patients with soem degree of cervical enamel projection. However, greater posttreatment horizontal and vertical attachment gains were observed in sites with a baseline cervical enamel projection.