Because of increased incidence of teenage births and high prevalence of lactation in Latin America, we determined the patterning of free amino acids (FAAs) in breast milk of 65 primiparous Ecuadorian women of varying ages (14-27 years). An automatic amino acid analyzer quantified levels of FAAs in milk samples obtained at three lactation stages: colostrum, transition, and mature milk. Regardless of mother's age, most FAAs increased with time postpartum, with taurine, glutamic acid, glutamine, and alanine being most abundant in all stages.