The presence of interleukin-12 (IL-12) in 39 samples of human milk was inve
stigated, using the enzyme-linked immunosorbent assay. IL-12 (>40 pg/mL) wa
s detected in 24 of the 39 samples collected (1408 +/- 2256 pg/mL, mean ? S
D, ra = 24). A range of concentrations of IL-12 was observed in colostrum,
transitional, and mature milk, with an apparent decrease in the mean concen
tration over time postpartum.