This study explores Carl Glickman's widely used Supervisory Belief Inventory (SBI). The inventory is presented in his text Supervision of Instruction: A Developmental Approach. The text suggests that the inventory is able to discern with some accuracy a teacher's or administrator's preference for one of three supervisory approaches--directive, collaborative, or nondirective. Glickman indicates that the SBI was designed initially as a "values clarification" exercise. Educators use the SBI for this purpose and for more substantive tasks (e.g., as a research tool). Despite the popularity of the text and the inventory itself, a recent analysis of the responses from nearly 700 cooperating teacher supervisors who completed the SBI shows that its three subscales fail to meet normal criteria for internal reliability, thus rendering suspect its ability to discriminate among these three supervisory approaches.