Meclomen (sodium meclofenamate) is a nonsteroidal anti-inflammatory drug (NSAID) with dual inhibition of both cyclooxygenase and lipooxygenase enzymes involved in arachidonic acid metabolism. Meclomen at nontoxic levels (10(-5) to 10(-8) mol/l) caused a 2-6 fold increase in interferon (IFN) production in lymphocytes induced by Sendai virus. This enhancement was observed in the case of all blood donors tested. Meclomen at the same concentration range had no effect on the antiviral activity of human IFN alpha. However, meclomen did show some enhancement of antiproliferative activity of human IFN alpha against human adenocarcinoma lung cells. Meclomen (10(-5) mol/l) inhibited intracellular levles of prostaglandin E2 by over 90% within the first four hours. The results presented here strongly suggest that inhibition of intracellular levels of PGE2 has no adverse influence upon the antiviral and antiproliferative activities of human IFN alpha.