We have recently examined the exons encoding the insulin receptor tyrosine kinase domain and GLUT 4 in 30 subjects with Type 2 (non-insulin-dependent) diabetes mellitus using a molecular scanning approach. The variant sequences Val-Met985 and Lys-Glu1068 of the insulin receptor and Val-Ile383 of GLUT 4 were each separately found in three different diabetic subjects. In a study of a Welsh population, the GLUT 4(383) variant was found in three of 160 diabetic and none of the 80 control subjects. In this study, the same group of Welsh Type 2 diabetic and control subjects was analysed using allele-specific oligonucleotide hybridisation, single nucleotide primer extension and allele-specific restriction digestion to ascertain the frequency of the two insulin receptor mutations. The Val-Met985 mutation was found in none of the 160 Welsh Caucasian Type 2 diabetic subjects and two of 80 control subjects. The Lys-Glu1068 mutation removes a Sty 1 site and digestion of amplified exon 18 with Sty 1 confirmed the presence of the mutation in the heterozygous state in the original subject. None of the Welsh diabetic or control subjects had the Glu1068 mutation. The discovery of a very common silent polymorphism at codon 130 of GLUT 4 allowed examination of the association of this locus with Type 2 diabetes using allele-specific oligonucleotide hybridisation in a subset of the Welsh subjects.(ABSTRACT TRUNCATED AT 250 WORDS)