Abstract Many available ELISAs lack the sensitivity required to reliably quantify levels of cytokines released in response to antigenic stimulation. In an effort to increase sensitivity of these assays, we compare the sensitivity of standard colorimetric ELISAs and corresponding chemiluminescent assays for three cytokines which are usually produced in very low quantities: mouse IL-12 p70, human IL-4 and mouse IL-4. Use of a chemiluminescent substrate enhanced the sensitivity of these assays 12–29-fold as compared to current colorimetric ELISAs. Accompanying this increase in sensitivity was an increase in dynamic range, a decrease in the time required to obtain maximum sensitivity and a decrease in the concentration of reagents required. These findings are of particular interest to those wanting to quantitate levels of any cytokine which is typically produced in low levels.