Nitric oxide and reactive oxygen species are important signal molecules that play key roles in plant defense responses. We investigated the involvement of nitric oxide elicitation in the synthesis of secondary metabolites within the adventitious roots of Echinacea purpurea. When roots were treated with $100{mu}M$ sodium nitroprusside (SNP), an exogenous nitric oxide producer, the accumulation of phenolics, flavonoids, and caffeic acid derivatives was enhanced. This level of SNP also induced an antioxidant defense, as indicated by increases in superoxide dismutase, ascorbate peroxidase, and ascorbic acid, along with decreases in hydrogen peroxide, lipid peroxidation, and dehydroascorbate/ascorbic acid. However, a higher concentration ($250{mu}M$ SNP) acted as a pro-oxidant, thereby raising the levels of hydrogen peroxide, lipid peroxidation, and dehy-droascorbate/ascorbic acid while diminishing ascorbic acid, ascorbate peroxidase, and the accumulation of secondary metabolites compared with our observations at $100{mu}M$ SNP. Therefore, we conclude that eliciting E. purpurea adventitious roots with a concentration of $100{mu}M$ SNP is beneficial to their accumulation of secondary metabolites.