Aim/hypothesis. Phosphatase and tensin homologue deleted from chromosome ten (PTEN) has recently been characterized as a novel member in the expanding network of proteins regulating the intracellular effects of insulin. By dephosphorylation of phosphatidyl-inositol-(3, 4, 5)-trisphosphate (PIP₃) the PTEN protein regulates the insulin-dependent phosphoinositide 3-kinase (PI₃K) signalling cassette and accordingly might function as a regulator of insulin sensitivity in skeletal muscle and adipose tissue. In this study we tested PTEN as a candidate gene for insulin resistance and late-onset Type II (non-insulin-dependent) diabetes mellitus in a Danish Caucasian population. Methods. The nine exons of the PTEN, including intronic flanking regions were analysed by PCR-SSCP and heteroduplex analysis in 62 patients with insulin-resistant Type II diabetes. Results. No mutations predicted to influence the expression or biological function of the PTEN protein but four intronic polymorphisms were identified: IVS1–96 A→G (allelic frequency 0.22, 95 % CI: 0.12–0.32), IVS3 + 99 C→T (0.01, CI: 0–0.03), IVS7–3 TT→T (0.10, CI: 0.03–0.18) and IVS8 + 32 G→T (0.35, CI: 0.23–0.47). The IVS8 + 32 G→T polymorphism was used as a bi-allelic marker for the PTEN locus and examined in 379 patients with Type II diabetes and in 224 control subjects with normal glucose tolerance. The IVS8 + 32 G→T polymorphism in the PTEN was not associated with Type II diabetes and it did not have any effect on body-mass index, blood pressure, HOMA insulin resistance index, or concentrations of plasma glucose, serum insulin or serum C peptide obtained during an oral glucose tolerance test (OGTT). Conlusion/interpretation. Variability in the PTEN is not a common cause of Type II diabetes in the Danish Caucasian population. [Diabetologia (2001) 44: 237–240]