A rapid lateral flow immunoassay screening method has been developed for the determination of sulfamonomethoxine (SMM) residues in swine urine. For this purpose, a specific monoclonal antibody (mAb), SMM4B9 for SMM, was generated and characterized. The mAb showed low cross-reactivity (not larger than 0.3%) to other sulfonamides and other potentially occurring analytes. Based on the competitive immunoassay principle, the strip was developed with the mAb SMM4B9 and applied to the screening of SMM residues. The test strip is made up of a sample pad, a gold-conjugate SMM4B9 reagent pad, a blotted test membrane containing a test line, a control line (a nitrocellulose membrane spotted with SMM-BSA and goat anti-mouse antibody, respectively), and an absorbent pad. The test could be accomplished within 8-10 min. It was shown that the sensitivity of the test strip was as low as 5 ng ml(-1) of SMM and the half of maximal inhibition concentration (IC50) was calculated to be 10.78 +/- 0.22 ng ml(-1) by relative optical density. In unaided visual assessment the detection limit of the strip was 15 ng ml(-1). For samples spiked at 20 and 30 ng ml(-1) the coefficient of variation (CV (%)) was between 2.3 and 7.1%. When the test strip was compared with high-performance liquid chromatography (HPLC) analysis for naturally contaminated swine urine samples, the difference in results was less than 6.1%. The data suggest that the method has advantages of high sensitivity, specificity, simplicity and speed of performance, as well as the characteristics of repeatability, reproducibility or accuracy and assurance. Therefore, the test strip is suitable to determine SMM residues in swine urine rapidly and reliably by quantitative, semi-quantitative or qualitative detection.