Many drugs are administered in racemic form and others undergo metabolism to form chiral metabolites. The chiral nature of most biologically important molecules inevitably results in differences between drug enatiomers in transport, binding and metabolism--hence differences in biological activity. Establishing a relationship between pharmacological activity, toxicology and stereoselectivity of metabolic processes may lead to the production of new and better drugs and to better use of present drugs. We have shown that stereoselective antibodies for warfarin, pentobarbital, secobarbital, thiopental and thiamylal can be obtained and utilized in radioimmunoassay (RIA) procedures for the determination of one enantiomer in the presence of the other. We are extending this work to cover other members of the class of coumarin anticaugulants and optically active barbiturates. We are synthesizing optically pure haptens based on drug molecules, conjugating them to protein and using the conjugates them to protein and using the conjugates to induce antibody formation. Optically pure drug enantiomers are radiolabeled and used in conjunction with the antibodies to develop stereoselective RIA's. The developed assays will be used to study differences in enantiomer disposition. Drug interaction effects, as well as effects of age, sex and disease, on enantiomer metabolism may be of clinical significance.