A double-blind, randomized, 2-wk experimental gingivitis clinical trial with cross-over design in 14 dental students was conducted in order to study the efficacy and safety of delmopinol hydrochloride solution (2 mg/ml), used with no other oral hygiene procedures, in comparison with placebo. Plaque formation was measured by the Quigley & Hein Plaque Index and gingivitis was assessed by bleeding on probing according to Mühlemann & Son. Rinsing with delmopinol resulted in lower plaque scores compared to placebo. The development of gingivitis was weak during the 2-wk test periods, and thus no conclusive results were obtained. As in previous studies, the most frequent adverse event when rinsing with delmopinol was a transient anaesthetic sensation in the oral mucosa. The results showed that rinsing with delmopinol hydrochloride solution (2 mg/ml) for 60 s twice daily with no other oral hygiene procedures led to less plaque formation than rinsing with placebo. This study also showed good tolerance and acceptability of mouthrinsing with delmopinol.