A technique of interlamellar keratoplasty was employed to evaluate the influence of difference in histocompatibility on the results of corneal transplantation in highly inbred rats. The degree of corneal clarity and vascularity and the incidence of rejection of relatively conpatible ("weak") and incompatible ("strong") allografts were recorded blindly in recipients with normal and vascularized corneas and in recipients sensitized with donor tissue either before or after corneal grafting. In contrast to the well-known effects of histocompatibility on skin and organ allografts, there was no substantial effect whatsoever of histocompatibility on either the severity of corneal allograft reactions orthe incidence of rejection. Consequently, the results of this experimental investigation suggest that tissue typing may have little or no value in clinical keratoplasty.