Antibody coated polystyrene beads were used to develop a solid phase radioimmunoassay for bovine dopamine β hydroxylase (EC 22.214.171.124). The technique is simple and offers many advantages over other radioimmunoassay techniques, including solid phase procedures, a major one being its adaptability to a wide range of antigen concentrations. Precision, sensitivity, and reproducibility compare favorably with those of existing methods. The ease and speed with which this test is performed have made it especially useful for clinical evaluations of serum dopamine β hydroxylase. Antibody coated beads should be applicable for the assay of other antigens.