A classification scheme and an instrument to determine work load, in use since June 1975 in the daily adjustment of supply and demand in the 24 pediatric units of the Sainte-Justine Hospital, Montreal, Quebec, is described. Construction and implementation of the instrument are delineated. The instrument was successful in determining the number of nurses necessary to meet the work load on various units. On the basis of these data, the short- and long-term management of supply and demand of nursing care was examined and the classification system was generalized to all types of patients except psychiatric.