How molybdate affects the chromatographic behavior of the glucocorticoid receptor on DEAE cellulose was investigated. Over the range 0-20 mM, molybdate caused a progressive change in the elution positions of both the transformed and untransformed receptor. At 20 mM molybdate, the transformed receptor eluted from the column before application of the KCl gradient. These changes were not due to an increase in conductivity of the buffer caused by molybdate; the conductivity at the peaks of elution were changed. Control studies with bovine serum albumen showed a similar effect by molybdate. Molybdate thus changes the chromatographic elution profiles of proteins. Failure to appreciate this fact can lead to errors in assessing the proportion of transformed and untransformed receptors in an extract.