A rapid test for the detection of IgM and IgG Epstein-Barr nuclear antigen (EBNA-1) has been extensively marketed. If IgM to Epstein-Barr viral capsid antigen (EBV VCA) is taken as evidence of current EBV infection, one observer detected 17 of 38 such samples and the other 22 of 38 as acute. The positive predictive value of the test was 63%, and the greatest difficulty was posed by the detection of IgM EBV VCA positive, heterophile antibody negative samples. Significant false positive results were obtained in sera with evidence of current Toxoplasma gondii, cytomegalovirus, and adenovirus infection. Rheumatoid factor was not a problem. Modification of the test protocol improved its performance: the positive predictive value rose to 87% and the negative predictive value to 81%. Although our modifications did not increase the speed of the test, there was reliable information on the EBNA-1 state. The test is best used as an adjunct to other EBV serology, and laboratories should be aware of the limitations of the rapid test.