Table 1. List of plants screened Plant Acalypha fruticosa Forssk. Actiniopteris semiflabellata Pic.-Ser. Alkanna orientalis (L.) Boiss. Carthamus tinctorius L. Centaurea pseudosinaica Czerep. Cleome schweinfurthii Gilg. Dodonaea viscosa (L.) Jacq. Forsskalea tinacissima L. Iris albicans Lange Jatropha variegata Vahl Lavandula pubescens Decne. Lippia citriodora Kunth Mentha longifolia (L.) Hudson Plectranthus hadiensis (Forssk.) Schweinf. ex Sprenger Tragia pungens (Forssk.) Muell.-Arg. YT-20 Verbascum bottae (Deflers) Huber-Mor. Mo-I08 F: Flower, L: Leaves, R: Roots or rhizomes, S: Stems, T: Fruits. aInformation of traditional use has been taken from native people. ethanol). After 30 min incubation at 25 C, the decrease in absorbance was measured at = 517 nm. The radical scavenging activity was calculated from the equation: Percentage of radical scavenging activity ¼ Abscontrol Abssample =Abscontrol 100 Cytotoxicity Assay The cytotoxicity of the investigated extracts was measured by the neutral red uptake assay (22) using FL-cells, a human amniotic epithel cell line. Only living cells are able to manage the active uptake of neutral red. The effect of the plant extracts on the proliferation of the FL-cells was determined in 96-well tissue culture plates. Confluent monolayers were incubated with different concentrations (serial dilutions) in medium for 72 h. The 50% cell- inhibitory concentration (IC50) was determined. Phytochemical Screening of the Methanolic Extracts The screening of chemical constituents was carried out with the methanol extracts using chemical methods and thin-layer chromatography (TLC) according to the methodology given in (23). Results This article describes the antimicrobial, antioxidant and cytotoxic activities of a number of plants from different localities used in Yemeni traditional medicine. A total of eCAM 2010;7(3) 325 Voucher specimen no. Family YH-05 Euphorbiaceae Part tested Traditional usesa L, S Skin diseases, malaria and wounds (3, 4, a) Mo-M08 Mo-I03 Mo-T10 Mo-S11 Mo-I01 Mo-T01 Mo-S08 Mo-I02 Mo-T05 Mo-S10 Mo-S03 Mo-M01 Mo-T04 Pteridophyta Boraginaceae Asteraceae Asteraceae Capparaceae Sapindaceae Urticaceae Iridaceae Euphorbiaceae Lamiaceae Verbenaceae Lamiaceae Lamiaceae L R L, S L, T L, S L, S L R L, T L, F L L, S L, R Wounds and burns (a) Common cold, pharyngitis, rheumatism and toothache (4, a) Skin diseases e.g. freckles, coloring agent and in food (4, a) Wounds, kidney diseases (4, a) Otitis (a) Malaria, wounds and burns (5, a) Diuretic and kidney diseases (a) Rheumatism and gout (4, a) Antiseptic, for wounds and hemostatic (3, 5) Antiseptic, carminative and diuretic, (3, 4, 5, a) Spasmolytic, gastrointestinal troubles, common cold and sedative (4, a) Spasmolytic and digestive disorders (3, 4, a) Antiseptic and haemostatic (3, a) Euphorbiaceae L, S Scrophulariaceae L, F Allergy and skin diseases (a) Cough, skin diseases and rheumatism (4, a) 34 extracts representing 16 plant species belonging to 11 families were submitted in the screening. Table 1 shows the botanical names, plant part used and the traditional uses of the plants in the collected areas. Characteristics of Plants The results of the antimicrobial activity of the investi- gated extracts are shown in Table 2. The antimicrobial activity of the studied plant extracts was exhibited mainly against the Gram-positive bacteria. None of the extracts showed any activity against Gram-negative bacteria. It was interesting to note that the multiresistant Staphylococcus strains showed more sensitivity to the investigated extracts than the other antibiotic susceptible Gram-positive bacteria. Generally, among the investi- gated extracts the methanolic extracts exhibited the highest antibacterial effect. The most pronounced activity with inhibition zones more than 14 mm was shown by the methanolic extracts of Acalypha fruticosa, Dodonaea viscosa, Jatropha variegata, Lippia citriodora, Plectranthus hadiensis (roots) and Tragia pungens (Table 2). The majority of the hot aqueous extracts of the antibacterial active plants did not express any activity or exhibited only low activity. It is remarkable that no extract showed any antifungal activity against C. maltosa. Antioxidant Activity The methanol extracts of six plants namely, A. fruticosa, A. semiflabellata, D. viscosa, P. hadiensis, T. pungens and