Plants of the Carex genus (Family: Cyperaceae) have attracted recent attention as potential food additives because they contain high levels of bioactive polyphenols commonly found in plant foods. Seven compounds, which included two resveratrol oligomers and five flavonoids, were isolated from seeds of Carex folliculata L. (northern long sedge), a forage prevalent in the northern United States. The compounds were identified by (1)H and (13)C nuclear magnetic resonance and mass spectrometry data. The resveratrol oligomers were pallidol (1), a resveratrol dimer reported to be present in levels equivalent to those of resveratrol in red wine, and kobophenol A (2), a resveratrol tetramer with a unique 2,3,4,5-tetraaryltetrahydrofuran skeleton. The flavonoids were isoorientin (3), luteolin (4), quercetin (5), 3-O-methylquercetin (6), and rutin (7). Compounds were evaluated for antioxidant activity in the diphenylpicrylhydrazyl (DPPH) radical scavenging assay; cytotoxicity activity against human colon (HCT116, HT29) and breast (MCF7, MDA-MB-231) tumor cell lines; and antibacterial activity against methicillin-resistant Staphylococcus aureus (MRSA). The antioxidant activities of the flavonoids (3-7; IC(50) values ranging from 50 to 200 microM) were comparable to that of ascorbic acid (IC(50) = 60 microM) and superior to those of the resveratrol derivatives (1 and 2; IC(50)>> 1000 microM) and butylated hydroxytoluene (BHT; IC(50) = 1500 microM), a commercial antioxidant. In the cytotoxicity and antibacterial bioassays, compounds 4 (IC(50) for HCT116 = 45 microM) and 6 (IC(50) for MRSA = 6.4 microM) were the most active, respectively. Therefore, given the wide availability and underutilization of C. folliculata, this forage may provide a source of bioactive compounds useful for nutraceutical purposes. Also, this is the first reported phytochemical investigation of C. folliculata.