A second follow-up of metabolic control and quality of life in insulin dependent diabetes mellitus (IDDM) patients who had switched 3 years before from syringe to multiple pen injection treatment, was carried out. A total of 73 consecutive outpatients were enrolled in the initial follow-up study in 1988, 1 year after their changeover to insulin pen, with their metabolic control and quality of life examined. The present study concerns the reexamination of 65 of them in 1990. Their HbA(1c) level was recorded yearly, already from 1987, on. After an enhancement of metabolic control in 1988, exhibited primarily by patients with fewer syringe injections before pen treatment, control up to 1990 was found to have regressed to about baseline level or to have gradually declined. Patients who perceived their ability to self-test blood glucose to have decreased exhibited the least satisfactory course of metabolic control. This is seen to indicate that maintaining self-testing in multiple injection insulin treatment is a very real challenge to this regimen.