Immunoassays based on the current available antibodies for large multi-sulfonamide screening programs have suffered from high selectivity for individual sulfonamides and a wide range of selectivities for different sulfonamides. In this study, five synthesized haptens, HS, BS, CS, SA10, and TS and two sulfonamides, SG and SMX were used as haptens, which may or may not contain a ring structure at the N1 position of the sulfonamides, were selected to evaluate the effectiveness for producing group-specific monoclonal antibodies (MAbs). Mice immunized with three different two-ring haptens were used for hybridoma production, which resulted in three unique MAbs recognizing 10, 13, and 15 sulfonamides showing 50 % inhibition (IC(50)) at concentrations below 100 ng mL(-1). MAb 4D11 derived from one novel immunizing hapten could recognize 12 sulfonamides with IC(50) values ranging from 1.2 to 12.4 ng mL(-1), almost within 1 order of magnitude. These produced MAbs show lower IC(50) values in addition to significantly improved group specificity compared with previously generated MAbs. This study clearly indicates that the careful selection of the immunizing hapten has an important effect on the specificity of the generated antibodies.