The investment seeks a high level of income exempt from federal income taxes by investing primarily in long-term low- to upper-medium-grade municipal securities. Normally, at least 80% of the fund's income will be exempt from federal income taxes. However, up to 20% of the fund's income could be derived from securities subject to the alternative minimum tax. It generally seeks higher yielding municipal bonds, including those that are rated noninvestment grade (BB and lower, or an equivalent rating) by a major credit rating agency or by T. Rowe Price, known as "junk" bonds.