Single urine voidings were collected twice a week in the clinical course of 12 low-birth-weight infants (gestational age: 31.8 ± 2.8 weeks; birth weight: 1,383 ± 308 g) and analyzed for 3-methylhistidine and creatinine. The mean 3-methylhistidine/creatinine ratio for 6 healthy, well-fed, growing low-birth-weight infants was 20.2 ± 1.9 µmol/mmol. In the clinical course of single individuals a rise of urinary 3-methylhistidine/creatinine ratio was observed in cases of acute infection and/or low energy supply (