Daredevils, many wearing traditional white clothing and red kerchiefs around their necks, tripped over each other or fell in the mad dash through the narrow, cobbled streets of the northern Spanish city of Pamplona.
A 23-year-old Japanese man from Okayama suffered bruises to his knee and elbow and a 36-year-old Pamplona native bruised his back and were taken to hospital for treatment, regional health authorities said.
None of the injuries was serious and the two men were expected to be discharged later in the day.
Several runners crashed against a wall in a curve along the route and were trampled by the bulls.
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"I managed to run alongside the bull and then fell over. Some bloke pulled me under the wooden fence and out of its way," said John Ross, 41, who came from Manchester for the festival and whose knees were bloodied from the fall.
"The first 15 seconds were good. Then I tumbled and people piled into me. I am the guy who people are going to blame for causing them to fall," he said at a bar near the bull ring after the run.
One young man dressed in white fell to the ground at the entrance to the bull ring and clasped his head in his hands as the bulls raced by.
"It was war. People pushed and grabbed on to you," said Javier Alvarez, a 23-year-old from Pamplona who wore a white Real Madrid jersey with the name of German midfielder Mesut Ozil on its back.
Another four Spaniards, were taken to hospital for various injuries, two of them in serious condition.
The San Fermin festival, a heady nine-day mix of partying and adrenaline-chasing, draws hundreds of thousands of people from around the world to Pamplona, a city of around 300,000 people.
It was made famous by Ernest Hemingway's 1926 novel "The Sun Also Rises".