In a previous paper, it was reported that Echinilin (Factors R&D Technologies, Burnaby, British Columbia, Canada) a formulation prepared from freshly harvested Echinacea purpurea plants and standardized on the basis of three known active components (alkamides, cichoric acid and polysaccharides) is effective for the treatment of a naturally acquired common cold. However, the mechanism by which this effect is achieved remains unknown. In the present study, Echinilin or placebo were administered to volunteers at the onset of their cold for a period of 7 days, with eight doses (5 mL/dose) on day 1 and three doses on subsequent days. Fasting blood samples were obtained before and during their colds. The decrease in total daily symptomatic score was more evident in the echinacea group than in the placebo group. These effects of echinacea were associated with a significant and sustained increase in the number of circulating total white blood cells, monocytes, neutrophils and NK cells. In the later part of the cold, the echinacea treatment suppressed the cold-related increase in superoxide production by the neutrophils. These results suggest that Echinilin, by enhancing the non-specific immune response and eliciting free radical scavenging properties, may have led to a faster resolution of the cold symptoms.