The daily insulin requirements as calculated with a closed-loop system (Biostator), were used for insulin infusion with a portable, miniaturized pump in 6 juvenile-onset, insulin-requiring diabetics. Three diabetics were given insulin in a manner like that of the Biostator, e.g., maximal insulin infusion about 1 hour after start of meals. The MBG was 8.7 +/- 3.9 (SD) mmol/l. Three other diabetics had insulin in a fixed profile with peaks beginning simultaneously with meals. MBG of these patients was 4.4 +/- 1.9 mmol/l. Knowing the daily insulin dosage as calculated from the Biostator, normal blood glucose levels can be achieved with a fixed profile of insulin given by a portable pump.