We have analyzed the EBV-related immune parameters of a healthy EBV-seropositive individual (ST) who has regular antibody titers but defective inhibitory capacity toward the growth of autologous EBV-infected B cells. This in vitro function reflects the EBV-specific memory because it does not occur in experiments performed with cells of seronegative individuals. An analysis of events following in vitro EBV infection showed that lymphocytes of ST behaved in some tests in the same way as those collected from seronegative individuals. These parameters were: lack of gamma-IFN production 24 hr after EBV infection; low production of soluble factors that inhibit EBV-induced B-cell proliferation; lack of generation of LCL selective cytotoxicity after repeated stimulation with autologous LCL; and high proportion of EBNA-positive cells in 7-day-old EBV-infected cultures. On the other hand, cellular memory to the virus detected by the production of IL-2 24 hr after infection, and by the production of LIF upon exposure to EBV-encoded antigens, conformed with the results obtained with seropositive individuals. T-cell-mediated inhibition of EBV-induced B-cell growth in vitro has been regarded as a corollary of in vivo control of EBV-infected B cells. However, it is absent or has a low efficiency in certain disease categories which are not accompanied by risk of B-EBV growth. Our results with a healthy individual also indicate that several mechanisms contribute to a harmless life-long virus carrier state.