The haptens p-tyramine and synephrine were conjugated to bovine serum albumin by means of the formaldehyde condensation reaction. These conjugates were emulsified in adjuvant and injected into rabbits. Antiserum was harvested at 10-day intervals after booster injections. The anti-sera were screened by immunodiffusion. After detecting the presence of antibody, an antiserum was further characterized by antiserum dilution curves, standard curves, and cross-reactivity studies using labeled p-tyramine or labeled metanephrine. The cross-reactivity studies indicated that the antisera to either hapten had low affinity to compounds with structural deviations on the side chain or ring other than at the position ortho to the phenolic hydroxyl group. The antisera were more sensitive to 3-methyoxylated compounds (3-methody-tyramine and metanephrine) than to 3-hydroxy or unsubstituted compounds.