We have assessed the capacity of continuous subcutaneous insulin infusion (CSII) to maintain good blood glucose metabolic control on Sundays, when waking is delayed, with reference to intensified conventional insulin therapy by multiple daily injections (MDI). The study lasted 3 weeks, including 3 week-ends. A total of 20 IDDM patients were selected for metabolic control: ten were treated by CSII and ten by MDI. Blood glucose was determined at least three times a day (fasting on waking, pre-lunch and pre-dinner). The times of blood glucose determinations and their values were recorded in a memory reflectance meter. Waking, the first blood glucose measurement and the first insulin injection (MDI) or bolus (CSII) were about 1 h later on Sundays than on a weekday (44 +/- 4 min in MDI group, P < 0.04; and 59 +/- 7 min in CSII group, P < 0.02). The times of the pre-lunch and pre-dinner blood glucose determinations were not significantly different. The mean waking and pre-lunch blood glucose values of the MDI group were higher on Sundays (11.5 +/- 3.8 and 9.7 +/- 4.5 mmol/l) than on weekdays (8.7 +/- 2.3 and 7.1 +/- 2.5 mmol/1)(P < 0.01). The pre-prandial blood glucose levels of the CSII group on Sundays and weekdays were not statistically different at any time. Changes in the waking time and the subsequent delay in the first insulin bolus on Sunday may alter blood glucose control in patients on MDI, but CSII allows such changes without any glycemic side effects.