The dot blot assay, modified and adapted for detection of antigens from Vibrio anguillarum in fish tissues, was specific for V. anguillarum and did not react with antigens of V. ordalii, Pseudomonas sp., or Yersinia ruckeri. The blot assay enabled detection of as little as 2.3 ng of a mixture of protein antigens obtained from cell-free extracts of V. anguillarum; it was about 100 times more sensitive than either the indirect fluorescent antibody technique or bacterial isolation for detecting V. anguillarum in fish tissues.