This paper analyses the intraday co-movements between returns on several commodity markets and on the stock market in the United States over the 1997-2011 period. By exploiting a new high frequency database, the authors compute various rolling correlations at (i) 1-hour, (ii) 5-minute, (iii) 10-second, and (iv) 1-second frequencies. Using this database, the authors document a synchronized structural break, characterized by a departure from zero, which starts in the course of 2008 and continues thereafter. This is consistent with the idea that recent financial innovations on commodity futures exchanges, in particular the high frequency trading activities and algorithm strategies have an impact on these correlations.