Evidence indicates that the glycemia-lowering effect of American ginseng root may be batch dependent. We therefore evaluated the effect of 5 root batches, representative of Ontario-grown American ginseng, on postprandial glucose and insulin indices. Twelve healthy subjects (5 male, 7 female), mean +/- SE age 26.5 +/- 2 years, body mass index 23.96 +/- 3.41 kg/m2, fasting blood glucose 4.77 +/- 0.04 mmol/L, were assigned to consume 9 g of American ginseng from 5 farms (A-E), administered in randomized sequence on 5 separate visits, and a water-control during the 6th and last visit. Treatments were consumed 40 min before a 2-hour 75-gram oral glucose tolerance test. Plasma glucose and insulin were measured at baseline, before, and during the test. Compared with control, batches A and C reduced glucose incremental area under the curve (IAUC) by 35.2% (156 vs. 240 mmol.min/L) and 32.6% (162 vs. 240 mmol.min/L), respectively. Batches A, C, and E reduced incremental peak glucose by 1.3, 1.2, and 1.1 mmol/L, respectively. Batch C reduced the insulin IAUC by 27.7% (15.8 vs. 21.8 nmol.min/L). Effects on glucose and insulin parameters were not different across ginseng treatments. The mean of the 5 ginseng treatments reduced peak postprandial glucose by 1.0 mmol/L, glucose IAUC by 27.7% (173 vs. 240 mmol.min/L), and insulin IAUC by 23.8% (16.6 vs. 21.8 nmol.min/L) relative to control. (All results statistically significant at p < 0.05.) American ginseng decreased postprandial glycemia and insulinemia; however, 40% of the batches did not reduce glycemia with the anticipated magnitude, irrespective of their saponin composition.