Major technical advances have occurred, especially in the last 5 years, in the laboratory diagnosis of viral infections. Immunologic detection of immediate early antigens in specimens such as bronchoalveolar lavage fluid and blood inoculated into shell vial cell cultures, particularly for herpesvirus (cytomegalovirus, herpes simplex virus, varicella-zoster virus), has provided results 16 to 48 hours after inoculation rather than the several days required for recognition of cytopathic effects in conventional tube cell cultures. Similarly, cytomegalovirus viremia can be detected directly by immunostaining of peripheral blood leukocytes with commercially available reagents the same day the specimen is submitted to the laboratory. Single-test membrane immunoassays have provided rapid (15 minutes) detection of viral antigens (respiratory syncytial virus, rotavirus, influenza virus type A). In the near future, diagnostic virology laboratories will be expected to monitor viral strains for susceptibility to the growing list of antiviral drugs. Amplification of nucleic acid sequences of viruses from cerebrospinal fluid or tissue, which generally does not yield isolates by conventional diagnostic techniques, has added a new dimension to the laboratory diagnosis of viral infection.