Using a sensitive high-performance liquid chromatography method, we quantified the concentration of polyamines (putrescine, spermidine, and spermine) in human milk as well as in a representative group of commonly used artificial infant formulas. Variations in polyamine levels were also analyzed in human milk during the immediate postnatal period. During the first week postpartum, putrescine levels in human milk remained very low and varied little, while spermidine and spermine concentrations rose markedly during the first 3 days, reaching plateau levels that were 12 and eight times higher, respectively, than the values measured on day 0. The mean total polyamine concentration was 557 +/- 18 nmol/dl with the following profile: spermine, 313 +/- 16; spermidine, 220 +/- 20; and putrescine, 24 +/- 3.5. In artificial powdered formulas, the polyamine concentration was approximately 10 times lower than in human milk, with no difference in putrescine and spermine contents between first-age and second-age formulas. By contrast, semi-elemental diets prepared by hydrolytic procedures using crude extracts of pancreatic enzymes were shown to be major sources of polyamines with a profile similar to that of human milk. Compared with first-age formulas, mean concentrations in spermine and spermidine were 39 and six times higher, respectively, in these semi-elemental diets, whereas putrescine levels remained almost equivalent in all types of milk tested. These data indicate that human milk and some semi-elemental diets provide substantial amounts of spermine and spermidine to neonates and infants that could potentially modulate intestinal maturation.