Capillary enzyme immunosorbent assay (CapELISA) is a modification of the standard enzyme immunosorbent assay which permits rapid detection of viral antigens in clinical specimens. The capillary tube format provides a very large reactive surface relative to the sample size. The close proximity of antigen to antibody in the tube optimizes the reaction, resulting in increased sensitivity and shorter incubation requirements. Sensitivity is further enhanced by use of a biotin-avidin enzyme detector system and a fluorogenic rather than a colorigenic substrate. The assay is performed at ambient temperature and requires less than 2 h. It is read with an inexpensive hand-held black light. Data for the use of CapELISA for the detection of herpes simplex virus in clinical specimens are presented. The results show greater than or equal to 85% sensitivity and 100% specificity when compared with tissue culture tests on the same samples. This new system should be advantageous for the diagnosis, treatment, and management of patients with herpesvirus infections and for the prevention of neonatal herpes acquired by passage of the fetus through an infected birth canal.