A simple procedure to estimate stress and its relation to malnutrition was developed based upon 24-h urine urea N excretion. This catabolic index partitions total urea excretion into that resulting from dietary protein intake and obligatory urea excretion and that due to an increase in endogenous protein catabolism: catabolic index equals 24-h urine urea N excretion (0.5 dietary N intake + 3 g) where an index of < 0 represents no significant stress; an index of 0-5, moderate stress, and an index > 5, severe stress. In 111 persons, significant differences were noted in the catabolic index, reflecting varying degrees of stress, nutrient intake and nutritional status. The catabolic index may have useful diagnostic and treatment applications.