The phenotypes of red cell glyoxalase I (GLO) were determined in two Icelandic population samples using starch-gel electrophoresis and high-voltage agarose-gel electrophoresis. The gene frequencies of 178 individuals were 0.46 for GLO1 and 0.54 for GLO2. In a group of Icelandic insulin-dependent diabetics the gene frequencies were found to be very similar. The evaluation of 30 mother-child pairs is also shown.