Acute dosing studies of aspartame, known commercially as "NutraSweet," have failed to demonstrate any neuropsychological changes that would imply performance decrements in flight operations. Such studies may be criticized on the grounds that the administration of a single, if large, dose of aspartame is not ecologically valid. Accordingly, a double-blind chronic dosing study of aspartame was conducted using ethanol (at 0.1% BAL) as the positive control. No detectable cognitive performance decrements were associated with the aspartame condition. However, the alcohol results exhibited a pattern of asymmetric lateral brain impairment that closely resembles that observed in studies of depressive patients. These results have operational implications as well as theoretical importance.