Four people have been injured as more than 1,000 thrill-seekers tested their agility and courage by racing alongside fighting bulls through the streets of Pamplona in the first run of this year's San Fermin festival.
Navarra Hospital said three people sustained head injuries while another suffered an arm injury. No-one was gored.
In the nationally televised morning runs, participants dash along with six bulls and accompanying steer down a narrow 930-yard course from a holding pen to Pamplona's bull ring.
The bulls then face matadors and almost certain death in afternoon bullfights.
Thursday's run lasted two minutes, 28 seconds.
The nine-day fiesta became world famous with Ernest Hemingway's 1926 novel The Sun Also Rises, and is now one of Spain's most important tourist events.
Many people suffered falls and were trampled by the bulls or other runners. In one incident, four bulls crashed into a bunch of participants close to the end of the race, and several people narrowly missed being gored.
Bull runs are a traditional part of summer festivals across Spain, and dozens of people are injured each year, mostly in falls.
Ten people were gored in last year's festival.
Fifteen have died from gorings in the San Fermin festival since record-keeping began in 1924.