An oligonucleotide-specific capture plate hybridization assay has been developed to rapidly, specifically, and sensitively detect Haemophilus parasuis from nasal swabs. Several in vitro studies have been performed to determine the sensitivity and specificity of the test, and in vivo studies have validated this technique in pigs. Results suggest that the assay detects <100 colony-forming units/ml in a pure culture and gives a positive result when H. parasuis is present in a ratio of 1:10(3)-10(4) in a mixed culture, and the probe does not hybridize with other related species found in the upper respiratory tract. This assay is more sensitive than culture for detection of the microorganism from nasal swabs and lesions.