A method for performing a multiplexed diagnostic assay, such as for two or more different targets in a sample, is described. One embodiment comprised contacting the sample with two or more specific binding moieties that bind specifically to two or more different targets. The two or more specific binding moieties are conjugated to different haptens, and at least one of the haptens is an oxazole, a pyrazole, a thiazole, a nitroaryl compound other than dinitrophenyl, a benzofurazan, a triterpene, a urea, a thiourea, a rotenoid, a coumarin, a cyclolignan, a heterobiaryl, an azo aryl, or a benzodiazepine. The sample is contacted with two or more different anti-hapten antibodies that can be detected separately. The two or more different anti-hapten antibodies may be conjugated to different detectable labels.