Beginning with the report of Ziff, Kibrick, Dresner, and Gribetz (2), evidence accumulated in recent years has indicated that urinary hydroxyproline excretion reflects collagen metabolism, since collagen is the only protein in the body that contains hydroxyproline in significant amounts (3). Ziff and co-workers, observing that the excretion of this amino acid in peptide form was greater in children than in adults, suggested that the level of urinary hydroxyproline might be related to the size of the metabolically active, soluble collagen pool available for breakdown. The results of a number of investigations (4-7) have supported this suggestion.In the present paper, further investigation of the relationship between growth and hydroxyproline excretion has been carried out in man. Urinary hydroxyproline has been determined in patients with normal, arrested, and accelerated growth, and in cases in which arrested growth has been stimulated by hormonal therapy. The data obtained indicate that the level of excretion of hydroxyproline shows a good correlation with rate of growth under all circumstances studied and, therefore, offers a useful and readily measured index of this phenomenon. METHODS AND MATERIALSNormal controls. Urines from normal children and adults were collected at home. In the 0-to 1-year group, the urine was collected in absorbent diapers with a special tissue paper sheet to isolate the feces. Diapers were changed six times in 24 hours. Upon removal, they were immersed in water saturated with toluene, and at the end of a 24-hour collection period, centrifuged in Hospitalized controls. Individuals with diseases in which marked alteration of collagen synthesis, breakdown, or excretion might be present were not accepted as controls. Accordingly, patients with anorexia, malnutrition, acute infection, renal disease, dystrophy, and inborn errors of connective tissue metabolism were excluded. Urines from hospitalized infants were collected by means of a metabolic bed or by use of a finger cot attached to polyethylene tubing.In eleven hospitalized, adult control subjects, the breakdown of diseases was as follows: myocardial infarction, 1; convalescent rheumatic fever, 1; inactive pulmonary tuberculosis, 2; post-delirium tremens, 1; osteoarthritis, 2; compensated alcoholic cirrhosis, 1; hypertensive cardiovascular disease, 1; arteriosclerotic heart disease, 1; and scleroderma, 1. In 44 hospitalized children, the following conditions were represented: club foot, 4; postpoliomyelitis under rehabilitation, 14; convalescent salmonellosis, 1; convulsive disorder, 3; inactive rheumatic fever, 1; convalescent meningitis, 4; post-arsenic poisoning, 1; convalescent pneumonia, 3; pes planus, 1; cystic fibrosis, 1; scoliosis, 1; croup, 1; inactive tuberculosis, 1; bronchitis, 3; rheumatoid arthritis, 1; infectious mononucleosis, 1; cellulitis, 1; psychiatric disorder, 1; and sicklecell anemia, 1.A gelatin-free diet was instituted at least one day before the collection period. Urines were collected under toluene and sampl...