Abstract Reagents for use in binding assays, particularly immunoassays, to determine diphenylhydantoin and for preparing reagents employed in such assays, including beta -galactosyl-umbelliferone-diphenylhydantoin conjugates, diphenylhydantoin immunogens, and N1, N3 and o-phenyl derivatives of diphenylhydantoin for preparing same. N1 and N3- omega -aminoalkyl and o-( omega -aminoalkoxy)-phenyl derivatives are prepared and coupled by amide linkage to a beta -galactosyl-umbelliferone derivative to form labeled conjugates useful in homogeneous or heterogeneous binding assays. N1 and N3- omega -carboxyalkyl and o-( omega -carboxyalkoxy)-phenyl derivatives are prepared and coupled by amide linkage to an immunogenic polyamino acid to form immunogen conjugates against which diphenylhydantoin-specific antibodies can be raised.