Ethrel (240 g L-1 ethephon, 2-chloroethylphosphonic acid) and gibberellic acid (GA3 and GA4+7) were applied to intact plants and excised tissues of 3-year-old American ginseng (' Panax quinquefolius' L.). The effects of these plant growth regulators on inflorescence and root development, floret abscission, root fresh weight and leaf chlorophyll were examined. Field-scale application of Ethrel (2.5-10.0 L acre-1) in mid to late June increased floret abscission. Ethrel at 2.5 L acre-1 applied in 100 gal acre -1 water, reduced red berry fresh weight by approximately 65%, increased total root fresh weights by about 15% and did not reduce leaf chlorophyll. Moderate to high concentrations of Ethrel (5.0-10.0 L acre-1 ) reduced leaf chlorophyll and root fresh weight. GA3 and GA4+7 (100-200 mg L-1) applied during bloom increased inflorescence expansion, and parthenocarpic development of the green berries. GA4+7 treatment increased root fresh weight by 8-12% and maintained leaf chlorophyll until late in the season. GA 3 and GA4+7 applied four times at 200 mg L-1 resulted in approximately 48 and 98% loss of perennating bud dormancy, respectively.