You can at Penson and ML Pro with a portfolio margin account. Bob Rmorse@victorsecurities.com 646-545-3860
With my broker I can't get my full margin with 3x ETF but I can get 2/3 of it. Which is twice my cash balance instead of 3x my cash balance. B careful, it takes ONE bad loss and your account is finished. Remember the US Downgrade? %7 down in one day x 3 = 21% then with margin x3 63%...... only one day