The influence of a 4 week course of balneotherapeutic treatment in Bad Hall on different blood parameters and on the activity of the antioxidative enzymes glutathione peroxidase (GSH-Px), catalase and superoxide dismutase (SOD) was examined in diabetics. The patients were divided into 2 groups. One group underwent an iodine-balneotherapeutic programme (therapeutic exercises, baths, packages, inhalations), the other group additionally received an iodine brine drinking cure. At the end of the cure, the cholesterol, triglyceride and glucose levels had fallen to normal values in both groups due to the diabetic diet and, if required, drug therapy. Erythrocyte SOD was also reduced in both groups. Plasma catalase and plasma GSH-Px were significantly raised only in the group drinking iodine brine, while erythrocyte GSH-Px and the amount of the lipid peroxidation product malonyl dialdehyde were unchanged. The observed improvements in the parameters are considered unspecific cure effects, which lead to a desirable normalisation and homogenisation. Only the enhancement of plasma GSH-Px activity can be interpreted as an iodine specific cure effect.