OBJECTIVES: The objective was to measure the total potentially available nucleosides (TPAN) in breast milk from Asian women. METHODS: One hundred sixty milk samples were collected from 135 healthy, lactating women in Hong Kong, the Philippines, and Singapore at four stages of lactation: colostrum (1 to 3 days postpartum), transitional (7 to 10 days postpartum), early mature (28 to 35 days postpartum), and late mature (90 to 100 days postpartum). Samples were pooled by site and stage of lactation before analysis. RESULTS: The mean TPAN concentration was 203 μM/L (69.4 mg/L corrected for recovery). Average TPAN concentrations were 171.9 μM/L in colostrum, 208.1 μM/L in transitional milk, 221.6 μM/L in early mature milk, and 210.6 μM/L in late mature milk, with no notable differences between countries. The major sources of nucleosides were RNA (43.3% of TPAN) and free nucleotides (39.9% of TPAN). The average percentages of cytidine, uridine, guanosine, and adenosine monophosphates were 44.5%, 23.1%, 16.5%, and 16.1% of TPAN, respectively. The sources of nucleosides and percentages of nucleotide bases were similar for all stages of lactation. Over 91% of the TPAN was present in the non-cellular component except in colostrum. CONCLUSIONS: The average TPAN level in Asian women is similar to that in European and American women, and free nucleotides in human milk represent less than half of the TPAN. © Elsevier Science Inc. 2003.