Nondestructive testing personnel in the nuclear industry are frequently questioned about the probability of flaw detection as a function of flaw size, location, and orientation.Nondestructive testing personnel are also questioned by fracture mechanics engineers concerning the accuracy with which the size of weld and HAZ defects can be determined, and if the degree of accuracy obtained will allow realistic fracture mechanics analysis of an existing defect once it has been detected.Because of a scarcity of actual data on the subject, these questions are presently being answered based on the opinions of various NDT experts. Unfortunately, these opinions vary widely and are substantiated only by personal experience.This report describes one facet of the effort to provide tangible data concerning the flaw detection capabilities of existing ultrasonic testing procedures and techniques.