Human breast milk has been observed to contain high concentrations of the chemotactic cytokines (chemokines) interleukin-8 (IL-8) and RANTES. Concentrations are greatest in colostrum, but are measurable in milk after several months of lactation. These chemokines are also found in the secretions of patients with galactorrhoea and in the "witch's milk" of the newborn. Chemokine levels show good correlation with the sodium levels but not with cell counts or the creamatocrit of the secreted milk. Mothers with pre-term deliveries show no statistical difference in chemokine secretion in comparison with those with term deliveries. Immunohistochemisty demonstrates IL-8 and RANTES immunoreactivity in the acinary epithelial cells of normal mammary tissue and IL-8 and RANTES were shown to be produced by cultured, human mammary epithelial cells (HMEC) after stimulation with different cytokines. These results suggest that mammary epithelial cells are the source of chemokines in human milk and that the recruitment of leukocytes in human milk is likely to be chemokine-driven.