An in situ nucleic acid hybridization (ISH) technique was developed to detect bluetongue virus (BTV) RNA in cell culture. The sensitivity of the ISH technique was compared with virus isolation (VI) and antigen detection, using an indirect fluorescent-antibody (IFA) or an enzyme immunocytoassay (EICA) technique, for detection of 5 BTV serotypes indigenous to the United States. The VI was the most sensitive technique, detecting BTV early after infection of the cells. The IFA and EICA were of similar sensitivity; BTV antigen could be detected shortly after demonstration of virus by isolation. The sensitivity of ISH for detection of BTV-17 was equivalent to that of antigen detection. The ISH was not as sensitive as VI or antigen detection when assaying for the other BTV serotypes.