The increasing use of medicinal herbs among the general public has piqued the need for scientific-based research to determine the mechanism of action of herbs administered orally in human subjects. The ability of three herbs, Echinacea purpurea, Astragalus membranaceus and Glycyrrhiza glabra, to activate immune cells in human subjects was assessed in this pilot study. The effect of these herbs when ingested for 7 days was measured both when administered singly, and in combination, using flow cytometry. The primary cell activation marker measured was CD69. The results demonstrate that Echinacea, Astragalus and Glycyrrhiza herbal tinctures stimulated immune cells as quantified by CD69 expression on CD4 and CD8 T cells. This activation took place within 24 h of ingestion, and continued for at least 7 days. In addition, these three herbs had an additive effect on CD69 expression when used in combination.