Medical personnel said 115 people taking part in a marathon Sunday in Hida, Gifu Prefecture, were stung by hornets, but no one suffered serious allergic reactions.
The runners were treated by doctors and ambulance attendants who were on standby along the marathon route, according to police.
A nest of yellow hornets was found under a bridge located along the route, firefighters said.
The runners were among 697 participants in the half-marathon section of the race, the event's organizer said. A total of 1,539 runners took part in the event.