Insulin glargine is a new extended-action insulin analogue, created by recombinant DNA modification of human insulin. Extension of the C-terminal of the B-chain with two arginine residues and the substitution of glycine for asparagine at position A-21 increases the isoelectric point, resulting in precipitation of the insulin at the injection site and a protracted absorption. Pharmacodynamic studies have demonstrated a prolonged metabolic profile without a pronounced peak and with a duration of action of 20 - 30 h. In clinical studies in people with Type 1 and Type 2 diabetes, insulin glargine has demonstrated improved pre-breakfast blood glucose control and a reduction in the frequency of hypoglycaemia, especially nocturnal hypoglycaemia, in comparison with neutral protamine hagedorn (NPH) insulin. In addition, 24h glycaemic control in Type 2 diabetes and treatment satisfaction may also be improved. However, whilst appearing achievable, insulin glargine has not yet demonstrated the ability to improve HbA(1c), though this may relate to inexperience in the use of the new compound. In order to fully exploit its metabolic advantages, it appears vital that the dose of insulin glargine should be titrated to achieve aggressive pre-breakfast blood glucose targets beyond those achievable with NPH in the absence of nocturnal hypoglycaemia. Insulin glargine appears to be a promising new addition to the insulin family and with increased experience in its use, especially in combination with rapid-acting insulin analogues, its full benefits may be realised. The use of insulin glargine with a rapid-acting insulin analogue brings us the closest we have ever been to providing the physiological insulin replacement that has long been awaited.