With progress in medical knowledge and in the technology of medical care, the contents of medical practice have become increasingly complicated year by year. The protocol practice (clinical algorithms or scheduled care) has been experimentally employed as one of medical-practice systems aimed at providing better medical care and maintaining its high standards. In the protocol practice the criteria for decision-making, which are clinically employed, are precisely made up in advance so that practice will be performed systematically. The WHO has recommended this protocol practice as a medical-care system appropriate for realizing clinical experiments. In recent years a number of clinical studies have been born from the protocol practice and, thus, it has been considered to be a formula for conducting clinical experiments tolerant of scientific criticism. The protocol practice, however, since it is difficult to conduct smoothly, has not yet been settled. This study aims at considering what we should do to make the protocol practice system settled through the observation of pitfalls in the course of its application.