In mammals and humans, noradrenaline is a key modulator of aggression. Octopamine, a closely related biogenic amine, has been proposed to have a similar function in arthropods. However, the effect of octopamine on aggressive behavior is little understood.An automated video analysis of aggression in male Drosophila has been developed, rendering aggression accessible to high-throughput studies. The software detects the lunge, a conspicuous behavioral act unique to aggression. In lunging, the aggressor rears up on his hind legs and snaps down on his opponent. By using the software to eliminate confounding effects, we now show that aggression is almost abolished in mutant males lacking octopamine. This suppression is independent of whether tyramine, the precursor of octopamine, is increased or also depleted. Restoring octopamine synthesis in the brain either throughout life or in adulthood leads to a partial rescue of aggression. Finally, neuronal silencing of octopaminergic and tyraminergic neurons almost completely abolishes lunges.Octopamine modulates Drosophila aggression. Genetically depleting the animal of octopamine downregulates lunge frequency without a sizable effect on the lunge motor program. This study provides access to the neuronal circuitry mediating this modulation.