A 3‐month clinical trial was conducted to compare the effects of two concentrations of a chlorhexidine mouthrinse on gingivitis and plaque accumulation. Six hundred (600) adults were divided into three treatment groups matched for age, sex, and initial gingivitis severity. Following a thorough examination and prophylaxis at baseline, subjects were given a mouthrinse containing either 0.12% or 0.20% chlorhexidine gluconate or a placebo mouthrinse. Subjects were evaluated after 6 weeks and 3 months of mouthrinse use. After 3 months, both chlorhexidine groups showed significantly less gingivitis and plaque than the placebo group. The group using the 0.12% chlorhexidine gluconate mouthrinse demonstrated 27–27 % less gingivitis occurrence and 28–28% less gingivitis severity than the placebo group. The 0.12% chlorhexidine gluconate group also had 48–48% less gingival bleeding and 36% less plaque than the placebo group. There were no significant advantages for the 0.20% mouthrinse over the 0.12% mouthrinse. It is therefore concluded that a 0.12% chlorhexidine gluconate mouthrinse offers the same clinical benefits as a 0.20% chlorhexidine gluconate mou