Spanish Red Cross spokesman Jose Aldaba said Tuesday that one person suffered a horn injury to the back and another was hit in the shoulder. It was not immediately known how serious the injuries were.
At least two other people were treated for injuries sustained in falls in the run.
The daily 8 a.m. runs see hundreds of thrill-seekers dashing ahead and alongside six bulls and their guiding steer through the narrow, cobblestoned streets of Pamplona to the city's bull ring.
Tuesday's race was the fastest so far at two minutes, 16 seconds. Two runs remain.
The festival draws hundreds of thousands of tourists each year.