Maternal milk is the first source of exogenous polyamines for the newborn. Polyamines modulate gut maturation in neonates, but no studies are available on polyamine concentration in human milk of preterm babies, even though they could be important for their immature gut. The present study aimed to determine polyamine concentration in human breast milk of mothers with preterm or term infants during the first month of lactation. Human milk samples were obtained during the first month of lactation from twenty-seven mothers with preterm babies and twelve mothers with babies born at term. The polyamine concentration in human milk was quantified by HPLC. During the first month of lactation, the total polyamine concentration was significantly higher in preterm milk than in term milk samples (7590 (SD 4990) v. 4660 (SD 4830) nmol/l, respectively (P ¼ 0·034)), as well as individual polyamine concentrations. Polyamine concentration in mature milk for preterm babies was significantly higher than that in mature milk for babies at term, and a similar trend was observed in colostrum and transition human milk. The spermidine/spermine ratio was higher in transition milk in preterm v. term samples, while in mature milk, the ratio was significantly lower in preterm than in term babies. In conclusion, the polyamine concentration was significantly higher in human milk for preterm than for term infants. This and the different spermidine/spermine ratios could influence the gut development of premature babies.