The fund generally invests at least 90% of its assets in the bonds of the underlying index and at least 95% of its assets in U.S. government bonds. It may invest up to 10% of its assets in U.S. government bonds not included in the underlying index, but which BFA believes will help the fund track the underlying index. It also may invest up to 5% of its assets in repurchase agreements collateralized by U.S. government obligations and in cash and cash equivalents.