This is a petition for mandamus by which petitioner seeks review of an order refusing a transfer to another district under 28 U.S.C. § 1404(a). The action appears to be an uncomplicated design patent case; the transfer is sought for the convenience of witnesses.

Petitioner makes a respectable showing. Nonetheless, we do not regard this an exceptional ease, warranting what is customarily characterized as extraordinary relief. The existence of interlocutory appeal procedure under 28 U.S.C. § 1292(b) of itself emphasizes the heavy burden on one who seeks mandamus on matters that come within the possible ambit of that statute.

The petition is denied. We do not determine the merits of petitioner’s claim. If it does reach us by ordinary process it will be open, if we find the district court committed error in refusing transfer, to consider compensation by way of reimbursement for the expense of bringing essential witnesses to Boston even though, on the ultimate issues, defendant does not prevail.