The present study aimed at investigating the influence of the time interval between injection of regular insulin and meal ingestion on postprandial glucose changes and overall blood glucose control in patients with type 1 diabetes on intensive insulin therapy. Fifteen C-peptide negative subjects were submitted, in a randomized order, to two 6-week treatment periods in which regular insulin was injected either 5 minutes or 30 minutes before each of the three main meals, in combination with a bedtime NPH insulin injection. The changes in plasma glucose excursions following a breakfast test (Cmax, Tmax, Cmin, Tmin, AUC0-240 min) were similar in the two experimental protocols. Furthermore, no significant changes were observed in daily insulin dosages nor in glucose profiles obtained using home blood glucose monitoring. Only a tendency to a greater 90-minutes postprandial increase in blood glucose levels was observed when regular insulin was injected 5 minutes rather than 30 minutes before meal. Glycated haemoglobin levels were similar after each treatment period (7.6 +/- 0.2% versus 7.5 +/- 0.2%; NS) and no differences in the incidence or severity of hypoglycaemic episodes were noticed between the two insulin schemes. In conclusion, in type 1 diabetic patients who are rather well controlled with a basal-bolus insulin scheme, the injection of regular insulin 30 minutes before each main meal provides no significant advantage as compared to the injection of regular insulin 5 minutes before meal.