In many hospital wards it is usual to have a certain proportion of the beds separately accommodated in single-bed rooms. Current practice shows a great variety not only in the availability of separate accommodation but also in the use made of such a facility. A clear understanding of both the demand and the way in which it can be met is of great importance in the theory and practice of ward design. This problem has been discussed in a recent paper by J. W. D. Goodall (1951), who, using purely medical criteria for the need for separate accommodation, considered that present practice was on the whole largely inadequate. He found it convenient to divide patients into two groups. First, those who have to be kept under close observation, such as dying cases, infants under 2 years, cases of posttraumatic psychosis, patients requiring special treatment, and so on. These are called type A patients, and their beds must be situated for easy observation and attention. Secondly, there are those who need to be separated but who do not require constant nursing supervision, such as patients who are liable to infect others or who are peculiarly susceptible to infection, burns cases and physically unpleasant patients, etc. These are of type B and need not be placed in such immediately accessible parts of the ward. Goodall obtained data from many different hospital wards showing the day-to-day demand for single rooms over, in most cases, at least a month.