Tear and serum concentrations of IgG, IgA, and IgM were estimated in serially drawn samples of 50 patients undergoing optical keratoplasty. Fifteen healthy individuals served as controls. Samples were collected at different postoperative intervals. An immunological rejection phenomenon was observed in nine patients. The rejection could be reversed in five of these nine cases. A decline in serum immunoglobulins was observed during the postoperative follow-up of these cases. This was unrelated to rejection phenomenon and was attributed to systemic steroid therapy. In tears, IgM was not detectable in majority of samples. No significant variation in tear IgA levels was observed between the cases where rejection was reversed and the ones in which it resulted in an opaque graft. In contrast, significant tear IgG increase was observed during the rejection phenomenon. The increased IgG levels returned to the basal value in each case in which rejection was reversed, but remained elevated much above basal and maximum control values in cases in which rejection could not be reversed. This differential response of tear IgG was highly significant. Our results suggest that raised tear IgG levels and its persistence despite therapy may be an indicator of corneal transplant rejection.