We have studied chemiluminescence produced by neutrophils stimulated by opsonized zymosan in insulin dependent (IDD) and non insulin dependent (NIDD) diabetic patients. Chemiluminescence was evaluated as the integral and maximum peak, total time and time to maximum peak of the response curve to opsonized zymosan. These values were then compared with circulating immune complexes (CIC) and glucose levels. Both IDD and NIDD patients had significantly higher values of chemiluminescence and CIC than normal controls. We also observed that patients who had the highest values of CIC and chemiluminescence levels were the ones with clinical microvascular complications.