Because most cytokines are utilized, catabolized, or excreted shortly after they are produced, it has been difficult to directly measure in vivo cytokine production. Consequently, it has been necessary to infer in vivo cytokine secretion levels from the results of ex vivo assays of cytokine secretion, assays that measure tissue levels of cytokine mRNA, or assays that stain tissues for cytokine protein levels. Results of these assays provide important and useful information, but do not necessarily reflect in vivo cytokine secretion. To better determine in vivo cytokine production, the in vivo cytokine capture assay (IVCCA) was developed. IVCCA facilitates measurement of cytokines in serum by increasing their in vivo half-lives. This increases the sensitivity of measurement of in vivo cytokine production 30- to 1,000-fold. The first protocol described in this unit is for luminescence-based ELISA, while the second is for an absorbance-based method.