This study probed the influence of antigenic exposure on the immunological response of the lacrimal gland. We utilized the germfree rat as a model system to monitor tissue and tear immunoglobulin changes following transfer of these animals into an antigen-laden, conventional environment. The number of IgA-and IgM-containing cells in the lacrimal glands of germfree rats was 5 to 8 fold less than that of conventional controls. This reduced immunological expression in germfree animals also extended to tear IgA levels, which were significantly decreased. No effect of germfree conditions was found on the tear content of secretory component (SC). Transfer of rats from a germfree to a conventional environment resulted in a significant increase in the number of IgA-and IgM-containing cells in the lacrimal gland. By four weeks after‘conventionalization’, the number of Ig-containing cells in lacrimal tissue was similar in both ex-germfree and conventional rats. In addition,‘conventionalization’led to a significant increase in the tear content of IgA: within four weeks following exposure to a conventional environment, tear IgA levels in ex-germfree rats were equivalent to those of age-matched, conventional controls. Overall, our results demonstrate that the secretory immune system of the lacrimal gland reacts to antigenic challenge with an increased immunological response.