Objective: To determine and to compare the levels of secretory immunoglobulin A in samples of colostrum and milk of mothers of term and preterm neonates. Material and Methods: The levels of secretory immunoglobulin A of 10 mothers of term neonates and 10 mothers of preterm neonates were determined from 5mL of colostrum or milk collected on the 1st, 4th, 10th and 15th days of the puerperal period, using the radial immunodifusion technique. We employed anamnesis, as well as physical and gynecological exams in women in the puerperal period. All the patients were attended at the Januário Cicco Maternity College. Results: The secretory immunoglobulin A levels were significantly higher in the colostrum and milk of mothers of preterm neonates when compared with the levels found in colostrum and milk of mothers of term neonates (Mann-Whitney test, p<0.0001). There was a significant decline in the secretory immunoglobulin A levels of the colostrum and milk of the mothers of term and preterm neonates during the four periods (Kruskal-Wallis test, p<00001). Conclusions: The secretory immunoglobulin A levels in colostrum and milk of mothers of preterm neonates were significantly higher than in the mothers of term neonates, demonstrating immunological adaptation in preterm neonate breast-feeding. © 2005 by The Brazilian Journal of Infectious Diseases and Contexto Publishing. All rights reserved.95357362Ferreira, T.R.B., Rispamonte, C., Stella, L.C., Albadalejo, R.G.C., Imunologia do leite materno (1998) Rev Perspectivas Médicas, 9, pp. 22-28Marques, R.F.S.V., Lopez, F.A., Braga, J.A.P., O crescimento de crianças alimentadas com leite materno exclusivo nos primeiros 6 meses de vida (2004) Jornal de Pediatria, 80, pp. 99-105Breastfeeding and the use of human milk (1997) Pediatrics, 100, pp. 1035-1039Lucas, A., Cole, T.J., Breast milk and neonatal necrotizing enterocolitis (1990) Lancet, 336, pp. 1519-1523Goldman, A.S., Garza, C., Nichols, B., Effects of prematurity on the immunologic system in human milk (1982) J Pediatr, 101, pp. 901-905Goldman, A.S., Chheda, S., Garofalo, R., Evolution of immunologic functions of the mammary gland and the postnatal development of immunity (1998) Pediatric Research, 43, pp. 1-15Schanler, R.J., Suitability of human milk for the low birth weight infant (1995) Clin. Perinatol, 22, pp. 207-222Hartmann, P., Cregan, M., Lactogenesis and effects of insulin-dependent diabetes mellitus and prematurity (2001) J Nutr, 131, pp. 3016-3020Neville, M.C., Anatomy and physiology of lactation (2001) Pediatrics Clinics of North America, 48, pp. 13-33Nascimento, M.B.R., Issler, H., Feeding materno: Fazendo a diferença no desenvolvimento, saúde e nutrição dos recém-nascidos de termo e pré-termo (2003) Rev Hosp Clin, 58, pp. 49-60Cutulo, L.R.A., Lamego, A.C., Fatores immunologicos da alimentação materno (1994) Arq Catar Méd, 23, pp. 191-198Chandra, R.K., Immunological aspects of human milk (1978) Nutr Rev, 36, pp. 265-272Carbonare, S.B., Carneiro-Sampaio, M.M.S., Composição do leite humano: Aspectos immunologicos (2001) Alimentação Materno, , Rego J.D. Rio de Janeiro: AtheneuFagarasan, S., Honjo, T., Regulation of IgA synthesis at mucosal surfaces (2004) Current Opinion in Immunology, 16, pp. 277-283(2002) Report of the Expert Consultation on the Optimal Duration of Exclusive Breastfeeding, pp. 28-30. , Geneva. SwitzerlandXantou, M., Immune protection of human milk (1998) Biol Neonate, 74, pp. 121-133Kunzs, C., Palmero, M.R., Koletzko, B., Jensen, R., Nutritional and biochemical properties of human milk, Paret II: Lipids, micronutrients and bioactive factors (1999) Clin Perinatol, 26, pp. 335-360Russel, M.W., Mestecky, J., Humoral immune responses to microbial infections in the genital tract (2002) Microbes Infect, 4, pp. 667-677Egmond, M.V., Damen, C.A., Spriel, A.B.V., IgA and IgA Fc receptor (2001) Trends Immumol, 22, pp. 205-211Barros, M.D., Carneiro-Sampaio, M.M.S., Milk composition of low birth weight infant mother (1984) Acta Paediatr Scand, 73, pp. 693-695Grumach, A.S., Carmona, R.C., Lazarotti, D., Ribeiro, M.A., Rozentraub, R.B., Racz, M.L., Weinberg, A., Carneiro-Sampaio, M.M.S., Immunological factors in milk from Brazilian mothers delivering small-for-date term neonates (1993) Acta Paediatr, 82, pp. 289-290Gross, S.J., Walkil, S., David, R.J., Faix, R.G., Buckleu, R., Elevated IgA in milk from mothers delivering preterm infants (1979) Pediatr Res, 13, p. 449