mGlu1 receptors are present in brain regions involved in aggression modulation. This study examines the effects of 3-4-Dihydro-2H-pyrano[2,3-b]quinolin-7-yl-(cis-4-methoxycyclohexyl)-methanone (JNJ16259685; 0.125, 0.25, 0.5, 1, 2, 4 and 8 mg/kg, i.p), a selective antagonist of the mGlu1 receptors, on agonistic interactions between male mice. Individually housed mice were exposed to anosmic "standard opponents" 30 min after drug administration. Ten minutes of diadic interactions was staged between a singly housed and an anosmic mouse in a neutral area. The encounters were videotaped and the accumulated time allocated by subjects to ten broad behavioural categories was estimated using an ethologically based analysis. JNJ16259685 (all doses) produced a significant reduction of offensive behaviours (threat and attack), without affecting immobility. These findings suggest for the first time a role for mGlu1 receptors in aggression regulation.