A panel of 24 healthy seropositive donors have been followed prospectively over a period of 15 months and monitored (1) for the level of EB virus shedding in the throat by means of a sensitive cord-blood transformation assay; (2) for the level of virus-infected B cells in the blood via a new in vitro protocol where "spontaneous transformation" can be seen to titrate against input cell number; (3) for anti-EB viral antibody titres and (4) for the prevailing level of virus-specific memory T cells in the circulation. Six donors shed easily detectable levels of EB virus into throat washings on every occasion of testing, whilst 16 other donors shed lower levels of virus detectable in throat washings on a majority (10 donors) or on a minority (6 donors) of test occasions; only 2/24 donors gave no evidence of virus shedding at any time. There was a direct relationship between the EB virus shedder status of an individual (i.e., the level of virus replication in the pharynx) and the number of infected B cells present in the circulation. These results indicate that chronic, usually low-grade, replication of the virus at some permissive site in the oro- and/or naso-pharynx is very often a stable accompaniment of the asymptomatic EB virus carrier state, and may indeed be essential for the long-term maintenance of that state.