A wind tunnel study was conducted to determine the effect of flat bar supports on the crossflow induced response of heat exchanger U-tubes. The 13-mm-dia tubes formed a triangular array with a pitch ratio of 1.57 and a mean U-bend diameter of about 1.5 m. A 0.3-m-long section of the array was exposed to a flow parallel to the plane of the U-bends. Experiments were conducted with no supports, with one set of flat bars at the apex, and with two sets of flat bar supports at the apex and 45 deg points. In each case, the tube response was monitored to a flow velocity beyond that required for fluid elastic instability. Limited experiments were also conducted to examine the effect of tube support clearance on tube response. Conclusions are drawn regarding the effectiveness of flat bars as U-bend antivibration supports.