Selenium and the selenium-dependent glutathione peroxidase (GSH-Px) were measured in healthy and diabetic children from Germany and Hungary. Hyperglycemia and hyperlipidemia are present in diabetes mellitus and they are associated with increased lipid peroxidation. The selenium content of erythrocytes, whole blood and plasma, as well as of plasma glutathione peroxidase activity, were found to be low in the healthy Hungarian children compared to the healthy Germans. Both groups of diabetics had significantly higher blood selenium (1.05 +/- 0.14 versus 0.86 +/- 0.1 mumol/L in Hungarians, 1.34 +/- 0.21 versus 1.12 +/- 0.22 mumol/L in Germans) and higher plasma selenium (0.89 +/- 0.15 versus 0.68 +/- 0.01 mumol/L in Hungarians and 1.01 +/- 0.2 versus 0.88 +/- 0.19 mumol/L in Germans) than the healthy children of the same countries. In all diabetic children the plasma glutathione peroxidase activity and triglycerides were higher and the plasma HDL-cholesterols (HDLC = high density lipoprotein-cholesterol) lower than those in healthy controls. The patients showed linear correlations between blood glucose and plasma glutathione peroxidase activity, as well as in erythrocyte glutathione peroxidase activity with triglycerides (TG) and an inverse correlation with HDL-cholesterol. Plasma selenium correlated only in healthy children with triglycerides, cholesterol and HDL-cholesterol. Irrespective of the geographical region diabetics had a higher selenium status than healthy children. In addition, we found correlations between selenium and lipoproteins in the reference group. The mode of glycation, oxidative procedures and the selenium binding to lipoproteins could explain the different associations in the healthy and diabetic children.