It has been observed protein carbonylation and glycation in the lens epithelial cell fractions of lenses in people with mature cataract. We used lenses of diabetic patients, weak and strong cigarette smokers and people who had senile cataract. The protein glycation is the highest in a diabetic senile cataract patients and the lowest in non-diabetic senile cataract patients. The protein carbonylation is extremely high in mitochondrial epithelial cells of the strong cigarette smokers. These results show that the glycation and carbonylation of the human lens proteins are the part of the cataract development in people. Specific factors, such as high glucose in diabetes and the tobacco smoke (in cigarette smokers), can change the lens structure, thus stimulating cataract development.