A radioimmunoassay procedure has been discovered for bupropion [(.+-.)-2-t-butylamino-3-chloropropiophenone], an antidepressant compound, in biological fluids. Novel compounds of formula ##STR1## wherein either R.sub.2 is oxygen and R.sub.1 is (CH.sub.2).sub.n -O-(CO).sub.m -(CH.sub.2).sub.p -COOH where n is an integer from 0 to 5, m is 0 or 1, and p is an integer from 1 to 4; or R.sub.1 is hydrogen and R.sub.2 is N-O-(CH.sub.2).sub.q -COOH where q is an integer from 1 to 3, and novel methods of making them and novel intermediates useful therein are disclosed. Novel immunogens for raising bupropion specific antisera, and novel methods of making them are disclosed comprising conjugates of the novel compounds and suitable carrier material. The drug is added to the antisera together with novel radiolabeled competitor of formula ##STR2## wherein R' is a suitable radioisotope as described above and R.sub.3 is hydrogen, R.sub.4 is Cl, and R.sub.5 is oxygen, or R' is hydrogen and either(a) R.sub.3 is H and R.sub.4 is Cl and R.sub.5 is NO(CH.sub.2).sub.q CO-X where q is as defined for formula I and X is a group having formula III ##STR3## wherein R.sub.6 is a suitable radioisotope as described above, R.sub.7 is hydroxyl, and s is an integer from 1 to 4;(b) R.sub.4 is Cl, R.sub.5 is oxygen, and R.sub.3 is (CH.sub.2).sub.n -O-(CO).sub.m -(CH.sub.2).sub.p -CO-X where n, m, and p are as defined for formula I and X is as defined above; or(c) R.sub.3 is hydroxy, R.sub.5 is oxygen and R.sub.4 is a suitable radioisotope as defined above.The measure of radioactivity of the antisera bound radiolabeled competitor provides a measure of the amount of drug in the assayed biological fluid sample. A standard curve can be constructed from which the amount of drug in the assay sample can be interpolated. A kit is disclosed for practicing the radioimmunoassay.