Fifty-two infants were enrolled in the study: 23 hypotrophically born infants (birth weight < 5th percentile according to Kyank) with present body weights < 3rd percentile according to Prader (group 1), 15 patients suffering from severe liver diseases (group 2), 14 patients without liver diseases (group 3). Usual serum parameters were estimated. Additionally, the hepatic detoxification capacities were measured using the non-invasive, non-radioactive [15N]methacetin urine test. 17 of the 23 infants of group 1 showed 15N elimination rates as low as in severe liver-diseased patients (group 2) whereas their serum parameters were in the normal range, as were those of group 3. The question remains whether intra-uterine malnutrition or postnatal effects, e.g., environmental conditions, caused the functional liver damage.