SummaryFull-term newborns (FTN) plasminogen was evaluated by different techniques (affinity chromatography, immunologic technique, casein method, and chromogenic substrate). The functional activity of the FTN plasminogen was about 50% of that of the adult. This suggests the possible existence of a functional anomaly of plasminogen in FTN.FTN plasminogen aminoacids were studied, and, besides small qualitative anomalies, a decrease in amino acid residues per mole of protein and a differentN-terminal amino acid were detected.SpeculationThe existence of a functional anomaly in full-term newborns plasminogen has been suggested. The possible role of this anomaly in the pathogenesis of the hemorraghic diseases of the neonate and in hyaline membrane disease is not known, thus, the identification of this anomaly could contribute to a better understanding of these diseases.