The effect of an acute period of moderate intensity exercise on maternal glycemic excursion following a mixed nutrient meal was studied. Five normal (NL) and six gestational diabetic (GDM) subjects were enrolled. A randomized crossover design was used to compare fasting glucose and insulin levels, peak glucose and insulin levels and incremental area of the glycemic and insulin curves following a mixed nutrient meal with or without an exercise stress that took place 14 h earlier. Exercise consisted of upright stationary cycling for 30 min at a heart rate consistent with 60% VO2max. The clinical characteristics of normal and gestational diabetic subjects were comparable. Mean values (+/-SEM) with, versus without, exercise for fasting glucose (NL: 78.9 +/- 2.6 vs. 80.0 +/- 2.6 mg/dl; GDM: 86.4 +/- 2.0 vs. 82.1 +/- 3.5 mg/ dl), peak glucose (NL: 132.3 +/- 10.4 vs. 139.1 +/- 15.6 mg/dl; GDM: 165.8 +/- 5.5 vs. 160.3 +/- 7.8 mg/dl), the area under the glycemic curve (NL: 5758 +/- 1038 vs. 6393 +/- 1281 mg/dl.min; GDM: 8,178 +/- 890 vs. 8,331 +/- 563 mg/dl.min) did not differ. Similarly, plasma insulin levels did not differ between protocols for either group of subjects. Exercise has been proposed as a treatment to reduce glycemia in gestational diabetes. Results from this study indicate a single bout of exercise did not blunt the glycemic response observed following a mixed nutrient meal.