The IL1R is composed of two kinds of molecule, type I (IL1R I) and type II (IL1R2). IL1R1 contributes to IL-1 signaling, whereas the IL1R2 has no signaling property and acts as a decoy for IL-1. In this study, we developed a bovine IL1R2-specific sandwich ELISA to examine the sIL1R2 concentration in serum and milk from dairy cows. The concentration of colostral IL-1 beta was examined to estimate the correlation to sIL1R2. The results showed that the sIL1R2 concentration in sera and milk changes with the stages of lactation. The serum sIL1R2 concentrations were 5.56 +/- 0.69 ng/ml (colostrum), 3.14 +/- 0.72 ng/ml (the early stage of lactation) and 5.76 +/- 1.25 ng/ml (the late stage of lactation). The milk sIL1R2 concentrations were 1.83 +/- 0.47 ng/ml (colostrum), 0.73 +/- 0.22 ng/ml (the early stage of lactation) and 2.92 +/- 0.56 ng/ml (the late stage of lactation). The concentrations of IL1R2 in sera and milk were significantly higher at the late stage of lactation and colostrum than that of the early stage of lactation. The reduction rates of sIL1R2 levels from the colostrum to the early stage of lactation were 43.6% (scrum) and 61% (whey). IL-1 beta was detected in all the colostrum (995.9 +/- 346.6 ng/ml). Significant correlation was observed between the levels of colostral IL-1 beta and IL1R2 (r = 0.75). (c) 2005 Elsevier Ltd. All rights reserved.