Cord serum concentrations of the N-terminal propeptide of type-III procollagen(PIIIP), insulin-like growth factor I (IGF-I), thyroid-stimulating hormone (TSH) and free thyroxine were measured in 149 neonates, consisting of 22 small for gestational age, 95 appropriate for gestational age, 21 large for gestational age and 11 neonates of less than 24 weeks of gestation. Their gestational ages (GAs) ranged from 20 to 41 weeks. A significant negative correlation was found between PIIIP levels and GA (r = -0.83, p less than 0.001). No significant difference was found in PIIIP levels between SGA and LGA neonates, when there were no difference in their GAs, in spite of a significant difference in their birth body weights (p less than 0.01). The high concentrations of the cord serum PIIIP did not appear to be influenced by either IGF-I or thyroid hormones, nor was there any relationship between PIIIP and the birth body weight, but only with GA, suggesting that determining cord levels of PIIIP seems to provide a useful parameter for the assessment of newborn maturity.