Yes, Running Can Make You High - New York Times

now medical technology has caught up with exercise lore. Researchers in Germany, using advances in neuroscience, report in the current issue of the journal Cerebral Cortex that the folk belief is true: Running does elicit a flood of endorphins in the brain. The endorphins are associated with mood changes, and the more endorphins a runner’s body pumps out, the greater the effect.