Investigations were carried out to clarify the role of autoimmune phenomena in the pathogenesis of human cataract. We determined the antibodies to lens proteins of serum in the following groups of patients: patients with senile cataract, patients with diabetic cataract, patients with diabetes mellitus, dependent of insulin and without cataract, patients without cataract and without diabetes mellitus (healthy adults), using the plate gel with double diffusion method described by Ouchterlony. 98% patients with senile cataract, 100% patients with diabetic cataract and only 12% healthy adults showed positive reactions to the test. There is little evidence so far, to incriminate immunological mechanisms in the pathogenesis of cataract.