This paper describes the evaluation of search units used to conduct a round robin ultrasonic examination of welds by the Pressure Vessel Research Committee's Subcommittee on Nondestructive Examination of Materials for Pressure Components. The round robin was intended to evaluate the effectiveness of ultrasonic examination of heavy section welds. Eighteen standard off-the-shelf search units were supplied by subcommittee members. Seven of these were rejected because they would have caused variations in test results. The search unit parameters and variables which affect amplitude response and thereby limit the repeatability of ultrasonic examinations are discussed. The test results obtained as a result of evaluating the eighteen search units are presented. A procedure for evaluating search units is discussed and the significant parameters identified. The variation in echo amplitude produced by inconsistent performance of search units is described.