The Sixth Circuit Court of Appeals has ruled on whether expert witness fees may be taxed as costs in federal court.
FRCP 54(d) permits a successful party to recover costs in federal court and 28 U.S.C. 1920 permits the recovery of "fees and disbursements for printing and witnesses." The amount recoverable for witnesses is spelled out in § 1821 and includes $40 per day for an appearance fee, allowable travel expense, and a subsistence allowance when overnight travel is required.
The Court determined that expert witness fees were not recoverable because § 1920 does not provide for them. However, the prevailing party may recover "as ordinary witness costs for attendance fees, travel expenses, and as a subsistence allowance under § 1821."
The case is L& W Supply Corporation v. Acuity, No. 05-6845 (6th Dir. Jan. 23, 2007). Read the opinion here.