Meclofenamate sodium was compared to other nonsteroidal antiinflammatory drugs in terms of its potency to inhibit the formation of 5-HETE and LTB4 in human leukocytes and the formation of prostaglandin E2 in bovine seminal vesicles as measures of its ability to inhibit the 5-lipoxygenase and cyclooxygenase pathways of the arachidonic acid cascade. Meclofenamate sodium was about 2-4 times less potent than BW-755C in inhibiting 5-lipoxygenase enzyme activity and three times more potent than benoxaprofen, while naproxen, ibuprofen, and indomethacin showed IC50 greater than 100 microM. Meclofenamate sodium and indomethacin were the most potent inhibitors of the formation of PGE2 in bovine seminal vesicles followed by ibuprofen, naproxen, and benoxaprofen in this order. Meclofenamate sodium, like BW-755C, can be considered a dual inhibitor of 5-lipoxygenase and cyclooxygenase pathways of arachidonic acid cascade. This finding may explain in part the antiinflammatory activity of meclofenamate sodium.