A screening method using tissue culture techniques determined inertness of ocular alloplastics. Secondary rabbit kidney cells revealed the presence of toxic constituents by absence of growth or cytopathic changes, or both. The optical portions of the lenses studied were nontoxic, whereas the polyamide loops of one lens were toxic. A keratoprosthesis that had been in situ in a patient for two years was highly toxic in culture. A neutralized agar overlay technique was not sufficiently sensitive to screen anterior chamber implants. The tissue culture technique, in combination with chemical, optical, and animal experimentation, may be helpful in determining which implant systems are most suitable for in vivo use.