A statement from the Navarra regional government said the four were Spaniards but none was in serious condition.
The run sees people racing with the bulls along a narrow 930-yard (850-meter) course from a holding pen to the city bull ring.
It lasted just over two minutes.
Dozens of people are injured each year in the "encierros," as the runs are called in Spanish. Most get hurt in falls.
Video of the run after the jump
