Interest on a private activity bond is not excludable from gross income under section 103(a) unless the bond is a qualified bond. The purpose of the private activity bond tests of section 141 is to limit the volume of tax-exempt bonds that finance the activities of nongovernmental persons, without regard to whether a financing actually transfers benefits of tax-exempt financing to a nongovernmental person. The private activity bond tests serve to identify arrangements that have the potential to transfer the benefits of tax-exempt financing, as well as arrangements that actually transfer these benefits. The regulations under section 141 may not be applied in a manner that is inconsistent with these purposes.