The formation of the elastic fiber was followed up in nine human aortas from foetus or newborn. During this period of ontogenesis an evolution of the elastic residue with increasing age was observed. There was a decrease in the association of structural glycoproteins or microfibrils with elastin. The insolubility of elastin increased with age, together with the increasing crosslinkage of the fiber, characterized by the ratio (sum of desmosines/lysine).