A Therapeutic Intervention Scoring System (TISS) is presented to allow quantitative comparison of patient care and research experiences of different intensive care units. 57 items of therapeutic intervention are scored on a one to four basis according to intensity of involvement. The points acquired per patient per 24 hours are summated by an experienced observer. TISS has been used to: 1) determine appropriate utilization of intensive care facilities at the Massachusetts General Hospital; 2) provide information on nurse staffing ratios for various patient care areas; 3) quantitatively validate a clinical classification of critically ill patients into four categories, thereby simplifying and organizing activities relating to patient care; 4) analyze cost of intensive care relative to the extent of care offered. Assumptions inherent in formulating this system are discussed. If other intensivists incorporate this system into their experience, meaningful comparisons between intensive care units can occur.