The value of a role in a profession is often tied to demand for and supply of practitioners in this role. Since a profession may seek to sustain its role's value by influencing supply of recognized practitioners, the National Commission for Health Certifying Agencies has included in its membership criteria a requirement for administrative independence between credentialing agencies and their related professional associations. Some roles are born of a clearly defined need; others evolve through a more complex sequence of events. After identifying some common, distinguishing traits among themselves, a group names these traits and establishes a set of membership criteria that may eventually replace the traits as distinguishing characteristics. Some individuals with the orginial traits may be excluded and form a second group. The two groups may be rejoined, and through role delineation the two levels of practitioners with the same performance characteristics may merge. The profession of respiratory therapy has followed this evaluation pattern. Role delineation efforts recommended that Certified Respiratory Therapy Technicians and Registered Respiratory Therapists be combined into one entry-level generalist position. Impact of conclusions of a role delineation must, however, be considered, especially regarding practicality of implementing a new or revised role in a profession. (YLB)