Randomised, double-blind, placebo controlled multicentre study. Patients were randomised to the treatment group with 600 mg ALA per day or the placebo group. At each examination we took stereo fundus photographs, HbA1c levels, and performed an ophthalmological examination. Primary endpoint of the study was the occurrence of clinically significant macular edema (CSME) within a follow-up period of 2 years.