A 30-year-old Briton was gored in the groin, while the Americans, 38 and 27, both sustained injuries to their armpits.
A total of 11 people – including three more Americans – were injured and taken to hospital at the opening run of the San Fermin festival.
Since record-keeping began in 1924, 15 people have died from gorings at the festival.
Thousands of adrenaline junkies flock to Pamplona every year for the nine day festival.
A total of eight, 8am bull runs take place, each lasting under five minutes over 825 metres in the town’s narrow, winding streets.
The festival comes to an end on July 14, with a party in the town’s streets.