The primary aim of patient classification is to be able to respond to the constant variation in patients' caring needs. Systems of patient classification usually include some form of time study, e.g. work sampling or time-and-motion studies. This article deals with the pros and cons of traditional time studies and with the theoretical bases of a new method of assessing the need for staff resources for nursing, a method termed 'Professional Assessment of Optimal Nursing Care Intensity Level'. The main idea of the method is to arrive at an optimal level of nursing care intensity for a ward by means of professional assessment and daily patient classification. The optimal level of nursing care intensity is supposed to prevail when there is a balance between the patients' need for care and the hospital's staff resources. The development of this new method and an account of a pilot study carried out in two wards are presented. The results of the pilot study established that the development of the method is worth continuing in order to create an administrative tool which, by its nature, is more compatible than traditional time studies with the idea of caring from the perspective of caring science.