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 4³⁸³ 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 this 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. The genotypic frequencies (homozygous wild-type and heterzygous polymorphic (poly) sequences) were not significantly different between diabetic and control subjects (Type 2 diabetic subjects: wild-type/wild-type 40%, wild-type/poly 46%, poly/poly 14%; Control subjects: wild-type/wild-type 37%0, wild-type/poly 45 %, poly/poly 18 %;p > 0.05). In conclusion, in a British Caucasian population the examined insulin receptor tyrosine kinase domain mutations are uncommon. Also the GLUT 4 locus does not appear to be strongly associated with Type 2 diabetes.