The widespread consumption of diets rich in anthocyanin and catechin content prompted the evaluation of their in vitro inhibitory effects on cyclooxygenase (COX) enzymes and on the proliferation of human cancer cell lines. Five anthocyanidins consisting of cyanidin (1), delphinidin (2), pelargonidin (3), peonidin (4), and malvidin (5) were tested for COX-1 and -2 enzyme inhibitory activities at 40 microM. Eleven catechins consisting of (+)-catechin (6), (-)-catechin (7), (+/-)-catechin (8), (+)-epicatechin (9), (-)-epicatechin (10), (-)-epigallocatechin (11), (-)-gallocatechin (12), (-)-epicatechin gallate (13), (-)-catechin gallate (14), (-)-epigallocatechin gallate (15), and (-)-gallocatechin gallate (16) were tested for inhibitory effects of COX-1 and -2 enzymes at 80 microM. Of the compounds tested, the galloyl derivatives of the catechins 11-15, cyanidin (1) and malvidin (5), showed the best COX inhibitory activities compared with the commercial anti-inflammatory drugs ibuprofen (at 10 microM), naproxen (at 10 microM), Vioxx (at 1.67 ppm), and Celebrex (at 1.67 ppm). Inhibition of the proliferation of the human cancer cell lines MCF-7 (breast), SF-268 (central nervous system, CNS), HCT-116 (colon), and NCI-H460 (lung) was evaluated at concentrations between 100 and 6.25 microM compared with the commercial standard, adriamycin (doxorubicin) at 6.25 microM. At 100-microM concentrations, anthocyanidins 1-5 and catechins 6-10 did not inhibit proliferation of the four cell lines. At 50-microM concentrations, catechins 12, 15, and 16 showed 95%, 100%, and 97% inhibition of breast cells, respectively. At 50-microM concentrations 12 and 16 were the most effective catechins against colon cells (85% and 93%, respectively) and lung cells (87% and 67%, respectively). CNS cells were the most sensitive of the test cell lines, and total growth inhibition was obtained with catechins 12 and 16 at 100-microM concentrations. Overall, only the galloyl derivatives of catechins 11-16 inhibited the proliferation of the cancer cell lines.