Recent advances in the care of low-birth-weight and preterm neonates have stimulated research into the best dietetic program to improve their survival and short/long term outcome. Some components of human milk that cannot be included in artificial formulas may be critical for survival. Of these, immunoglobulins are important, and in particular secretory immunoglobulins A (sIgA). The concentration of secretory IgA was measured by immunoblotting (an immunoelectrophoretic technique having high specificity and reliability) in milk from mothers delivering at term (TM) or prematurely (PM). In both groups, IgA concentrations were high very early on but quickly decreased during the first week of lactation. The early IgA mean concentration was higher in PM than in TM but, because of high variability in PM milk, the difference rarely reached statistical significance. This variability during lactation reflects the important role of human milk in supplying immunological factors to cope with the gastrointestinal absorption of high molecular weight proteins in the first days of life. Immunological protection is particularly critical for a preterm baby, so it is important to promote feeding with its own mothers milk if possible, paying strict attention to the timing of milk collection.