Utilizing a nonhuman primate model, a study was carried out to determine the nature of the attachment between the tooth and the gingival tissues following periodic root planing and soft tissue curettage. Under the conditions of this investigation, periodic root planing and soft tissue curettage combined with thrice weekly plaque control resulted in the formation of a long junctional epithelium with no new connective tissue attachment. In eight of the 22 experimental pockets, however, this procedure produced discontinuities or "windows" in the junctional epithelium. The coronal attachment of gingival tissues to the root surface (increased resistance to probing) commonly reported following root planing and soft tissue curettage appears to result from the formation of a long junctional epithelium rather than new connective tissue attachment.