<p>Male crickets produce a distinctive aggression song when engaged in contests with conspecific rivals. We studied the effect of asymmetries in singing ability on the intensity and outcome of fights among pairs of male <i>Acheta domesticus</i> crickets. We experimentally muted males by brushing warm beeswax on their stridulatory file. These males were able to move their wings normally but were unable to sing. Unmuted males had beeswax applied on the forewing but away from the stridulatory file, allowing them to sing normally. We show that among size-matched males, fights between two muted males were significantly more intense compared to fights in which at least one male could sing. Moreover, when males were size matched but asymmetric in singing ability, singing males won every contest that had a discernible winner. When males were mismatched by body size, larger males initiated aggression most often and won most fights but the advantage of larger size was diminished when males were unable to sing. Singing males tended to initiate aggression against muted males. Although larger males won more fights overall, among contests with asymmetry in singing ability, the larger-male advantage diminished from 94% when they could sing, to only 50% when muted. Our results show that aggression song mitigates the cost of fighting by resolving conflict at lower levels of aggression. They also show that aggression song reinforces effects of differences in body size, suggesting that aggression song may signal male resource holding potential.</p>