This study aimed to examine the carbohydrate content (monosaccharides, lactose, and oligosaccharides) of human milk over 4 months of lactation to determine whether any changes occurred over time. Milk samples from 46 mothers, who delivered at term, were collected at 4th, 10th, 30th, 60th, 90th, and 120th days after delivery. Carbohydrates were measured by high-pressure liquid chromatography. Mean lactose concentration (+/- SD) increased from 56 +/- 6.06 g/L on day 4 to 68.9 +/- 8.16 g/L on day 120. Oligosaccharide level decreased from 20.9 +/- 4.81 g/L to 12.9 +/- 3.30 g/L, respectively. Monosaccharides represented only 1.2% of total carbohydrates. The changes in carbohydrate composition found indicate that carbohydrate synthesis by the mammary gland is a dynamic process. The physiological and biological relevance of human milk oligosaccharides is also discussed.