With the increasing popularity of the use of cytokine immunoassays in basic and clinical research, there is an urgent need for cytokine immunoassay reference preparations and standards in order that results published by various investigators can be directly compared. Until such standards are available, it is recommended that results obtained using immunoassays from different sources be compared with caution. Additionally, users of immunoassays should clearly understand the biology of the systems they are studying and the characteristics of their immunoassays with respect to cross-reactivities with cytokine isoforms, interferences by soluble receptors, and matrix effects on samples of interest. It is also recommended that immunoassay developers take special precautions in the selection of antibodies and only use antibodies that are not biased against one or the other of the recombinant forms.