The fund invests at least 80% of its assets in a diversified portfolio of debt securities whose interest is, in the opinion of bond counsel for the issuer at the time of issuance, exempt from federal income tax ("Municipal Bonds"). It may invest 25% or more of its total assets in Municipal Bonds that finance similar projects, such as those relating to education, health care, housing, transportation, and utilities, and 25% or more of its total assets in industrial development bonds.