Sixty-two subjects having either insulin-dependent or non-insulin-dependent diabetes completed a randomized, double-blind study comparing effects of aspartame or a placebo on blood glucose control. Twenty-nine subjects consumed 2.7 g aspartame per day for 18 wk, given as aspartame-containing capsules with meals, while 33 subjects took identical appearing placebo capsules. After 18 wk, no changes were seen in fasting or 2-h postprandial blood glucose levels or glycohemoglobin levels in either the aspartame- or placebo-treated groups. Adverse reactions were no more common in the group taking aspartame. We conclude that use of aspartame as a low-calorie sweetener does not adversely affect glycemic control of persons with diabetes.