The purpose of this study was to assess the efficacy of supragingival irrigation with 0.06% chlorhexidine gluconate (CHX) on naturally occurring gingivitis. The relative benefit of CHX irrigation in comparison with CHX rinsing, water irrigation, and normal oral hygiene was evaluated. In a blind, placebo-controlled 6-month study 222 patients were assigned to one of four groups: Group 1: Once daily irrigation with 300 ml water followed by irrigation with 200 ml 0.06% chlorhexidine gluconate (experimental); Group 2: Twice daily rinsing with 15 ml 0.12% chlorhexidine (positive control); Group 3: Once daily irrigation with 500 ml water (irrigation control) and Group 4: Sodium fluoride dentifrice for normal oral hygiene only (negative control). All groups used the same sodium fluoride dentifrice for tooth brushing. At baseline, 3 months, and 6 months patients were examined for Gingival Index (GI), Bleeding on Probing (BOP), Plaque Index (PLI), Pocket probing depth (PD), Calculus Index (CI), and stain. After the baseline visit all patients received a supra- and subgingival oral prophylaxis. At 6 months GI and BOP were significantly (P less than or equal to 0.05) reduced by adjunctive CHX irrigation (42.5% and 35.4%, respectively), CHX rinse (24.1% and 15.0%), and water irrigation (23.1% and 24.0%) compared to tooth brushing alone. Plaque was significantly (P less than or equal to 0.05) reduced only by CHX irrigation (53.2%) and CHX rinse (43.3%) while calculus and staining were significantly (P less than or equal to 0.05) increased in the two chlorhexidine groups (276.4% (irrigation) and 273.2% (rinse)). Although significant (P less than or equal to 0.05), pocket probing depth reduction was minimal after CHX irrigation (4.6%).(ABSTRACT TRUNCATED AT 250 WORDS)