We describe five murine monoclonal antibodies that are specific for human IL-4. At least three spatially distinct epitopes on the hIL-4 molecule are recognized by this panel of antibodies which allowed development of a sensitive sandwich EIA specific for hIL-4. The EIA is capable of detecting 200 pg/ml of hIL-4 and exhibits no detectable crossreactivity to seven other human cytokines examined. In addition to the EIA these antibodies are also useful in a number of other techniques for investigating hIL-4. Recombinant hIL-4 can be easily and efficiently purified by affinity chromatography using these mAbs. Western blotting with two of the antibodies detects as little as 1.8 ng/ml of hIL-4 in a 50 μl sample. Finally, we present a method for cytoplasmic localization of hIL-4 by a fluorescence staining method utilizing a hIL-4 specific mAb.