Six methanol extracts from different parts of plants used in northeast Mexico as general health supplements were examined for their potential as antioxidants. The plants evaluated were: Turnera diffusa Wild. (Turneraceae), Cucurbita foetidissima Kunth (Cucurbitaceae), Flourensia cernua D.C. (Asteraceae), Selaginella pilifera A. Braun (Selaginellaceae), Juglans mollis Engelm. (Juglandaceae) and Centaurea americana Nutt. (Asteraceae alt. Compositae). Antioxidant properties of these extracts were evaluated by means of different assays, including the l,l-diphenyl-2-picrylhydrazyl radical test by TLC and spectrophotometry, inhibition of xanthine oxidase (XO) activity, and total phenolics content. Five plants showed high scavenging potential; their total phenolics content was also high. The extracts from four plants inhibited the activity of XO. Two of the most promising plants, T. diffusa and J. mollis, did not show cytotoxicity. Considering that antioxidants prevent lipid peroxidation in foods and help in the treatment and prevention of degenerative illness, these two species are good candidates to be considered and further evaluated as natural additives in foods to provide protection against oxidative degradation.