New derivatives of 3-oxoolean-1-en-28 oic acid and 3-oxours-1-en-28-oic acid were synthesized. Nine of them showed significant inhibitory activity against interferon-gamma-induced nitric oxide production in mouse macrophages when assayed at the 1 mu M level. 3,12-Dioxoolean-1,9-dien-28-oic acid (3) had the highest activity (IC50, 0.9 mu M). (C) 1997 Elsevier Science Ltd.