Insulin glargine is a long-acting insulin analogue, with a longer duration of action and a flatter time-action profile compared with NPH insulin. These properties can be predicted to result in higher glucose levels during the night and lower glucose levels after dinner following bedtime injection of insulin glargine compared with an equal dose of NPH insulin injected at bedtime. In two large-scale clinical trials involving either insulin-naïve (426 patients treated for 1 year) or previously insulin-treated (518 patients treated for 28 weeks) patients with type 2 diabetes, comparing addition of once-daily insulin glargine or NPH insulin to oral agents, these predictions were proven to be correct. Nocturnal hypoglycaemia was reduced by 58% in insulin-naive patients and by 22% in previously insulin-treated patients, and dinner-time glucose control was significantly better with insulin glargine than with NPH insulin once daily in the study in insulin-naive patients. The 'treat-to-target study' (756 insulin-naive patients treated for 24 weeks) showed that good glycaemic control can be achieved with aggressive titration of the insulin dose with either once-daily insulin glargine or NPH insulin combined with oral agents (mean endpoint HbA(1c) was 6.96% with insulin glargine and 6.97% with NPH insulin); however, this was achieved with less variability and nocturnal hypoglycaemia with insulin glargine. These data support use of insulin glargine instead of NPH insulin for basal insulin replacement in patients with type 2 diabetes.