Abstract The 6-(0-carboxymethyl) oxime derivatives of 6-oxomestranol and 6-oxo-17α- ethynylestradiol were prepared from 3-methoxy-6-oxoestrone. These haptens were then coupled to bovine serum albumin by the mixed anhydride technique to yield the steroid- protein conjugates required for the production of specific antisera for the radioimmunoassay of mestranol and 17a-ethynylestradiol. In addition we have described the preparation of ...