The Transfusion Medicine Tutor (TMT) has been designed to study the use of computers in teaching concepts and problem- solving skills important in the field of clinical laboratory science. This system provides students with an opportunity to gain experience by solving a wide range of actual cases, and coaches these students when they are having difficulties. This system is designed specifically to detect and respond to a variety of errors that students may make while solving cases, and to suggest more advanced problem-solving methods when appropriate. This article describes the concepts behind the design of TMT.