CERTIFICATION PURSUANT TO RULE 30A-2(B) UNDER THE 1940 ACT AND SECTION 906 OF THE SARBANES-OXLEY ACT I, James D. Dondero, Chief Executive Officer of Highland Institutional Floating Rate Income Fund (the "Registrant"), certify that: 1. The Form N-CSR of the Registrant (the "Report") fully complies with the requirements of Section 13(a) or 15(d) of the Securities Exchange Act of 1934, as amended; and 2. The information contained in the Report fairly presents, in all material respects, the financial condition and results of operations of the Registrant. Date: APRIL 26, 2006 /S/ JAMES D. DONDERO ------------------------- ------------------------------------------- James D. Dondero, Chief Executive Officer (principal executive officer) I, M. Jason Blackburn, Chief Financial Officer of Highland Institutional Floating Rate Income Fund (the "Registrant"), certify that: 1. The Form N-CSR of the Registrant (the "Report") fully complies with the requirements of Section 13(a) or 15(d) of the Securities Exchange Act of 1934, as amended; and 2. The information contained in the Report fairly presents, in all material respects, the financial condition and results of operations of the Registrant. Date: APRIL 26, 2006 /S/ M. JASON BLACKBURN ------------------------- ------------------------------------------- M. Jason Blackburn, Chief Financial Officer (principal financial officer)