Intensive metabolic control of diabetes is probably important during formation of the embryo early in pregnancy. The purpose of this study was to determine the efficacy and complications of continuous subcutaneous insulin infusion therapy during the fifth to the tenth week of gestation. Twenty-four insulin-dependent subjects were trained to use blood glucose self-monitoring and the Auto Syringe portable insulin infusion pump (AS6C). Regular insulin was administered as a basal infusion of 18 +/- 8 U/24 hours (+/- SD) (12.2 +/- 3.9 mU . kg-1 . h-1) and as bolus injections of 6 +/- 3 U before meals and 1.2 +/- 1 U before snacks. Reasonable control of fasting (119 +/- 30 mg/dL) and postprandial (133 +/- 34 mg/dL) hyperglycemia was achieved, accompanied by an average of 2.2 +/- 1.5 symptomatic hypoglycemic episodes per week. The frequency of complications with this new therapy declined as the authors gained experience in teaching the system. The persistence of good diabetic control in many of the subjects after they returned to conventional insulin therapy points to the need for a controlled trial of continuous subcutaneous insulin infusion therapy versus intensive conventional therapy in pregnancy.