In 1968, 21 continuous lymphoblastoid tissue culture cell lines were established in this laboratory from the peripheral blood of individuals with diagnosed acute infectious hepatitis (IH) (1). Concurrent attempts to establish similar cultures from normal subjects yielded a significantly lower number of continuous lines. These lines have been maintained in rapidly dividing suspension culture for 9 to 12 months. Similar cell lines have been derived from individuals with lymphoma, leukemia (2, 3) infections mononucleosis (4), serum hepatitis (5) and other infectious diseases (6) as well as from presumably normal “healthy” donors (7, 8). Most have been shown to contain the Epstein-Barr virus (EBV), a herpes-like virus. The present report summarizes studies employing immunofluorescence (IF) and electronmicroscopic techniques to determine whether EBV or any other viral agents were present in our cell lines which could be associated either with IH or with the lymphoproliferative phenomenon observed in vitro by leukocytes from patients with IH.