An IF technique for the detection of HSV antibodies by using a lymphoblastoid cell line, Raji(A44), which continuously produce a constant amount of HSV antigen, is described. IF and IH tests were found to be similar with respect to sensitivity and reproducibility. Sero-conversions detected by the CF test were detected with this cell line. The Raji(A44) line (cells in suspension) can be routinely used for the diagnosis of HSV infection.