This trial tested the adjunctive effects of a 0.12% chlorhexidine rinse (Peridex) upon gingival healing following scaling and root planing. Assessments were made on reduction in plaque (Pl), gingivitis (GI), pocket depth and gingival bleeding as measures of treatment benefit. All subjects had Class II, III or IV periodontal conditions. Following baseline examinations, subjects received a gross supragingival scaling and polishing. Subjects were separated by sex and periodontal classification, arrayed by GI scores, and randomly assigned to either the chlorhexidine rinse or a placebo rinse. Subjects were instructed to rinse with 1/2 ounce of their assigned products for 30 seconds twice daily. Following two weeks of product use, the clinical examinations were repeated and two randomly selected, opposing contralateral quadrants were scaled and root planed. After two more weeks of product use (week 4), clinical examinations were repeated and the remaining quadrants were scaled and root planed. At week 6, final clinical examinations were conducted. Since half-mouths were treated at different times and exposed to the treatment rinses for different periods, the data were analyzed for the half-mouths independently 2 and 4 weeks after gross scaling, and 2 and 4 weeks after root planing. A total of 94 subjects (47 in each treatment group) completed all phases of the trial. Gingival healing following scaling and root planing in subjects using a chlorhexidine rinse (0.12%) was significantly better than subjects using the placebo rinse as evidenced by less gingivitis (29%), fewer GI bleeding sites (48%) and less plaque (54%).