Several newly developed methods, including immunological and DNA hybridization techniques, have been recently introduced in clinical diagnosis. Target molecules for these detection methods are either avirulent materials or virulence factors specific to the individual causative pathogen. Examples requiring the detection of bacterial virulence factors for the accurate identification of causative agents are increasing; for example differentiation of enterotoxigenic Escherichia coli from nonpathogenic E. coli, and identification of cholera toxin-producing (or non-producing) V. cholerae 01. Recent progress in the detection of virulence factors is described. Advantages and disadvantages of various detection methods of bacterial virulence factors are also discussed.