Sequential potentiation of antiinflammatory activity of dexamethasone was obtained by co-administration of diclofenac-Na (and indomethacin), but not of phenylbutazone and, apparently, of acetylsalicylic acid (ASA) in the carrageenin rat paw edema. In the adjuvant arthritic rat, additive effects were only seen. Co-administration of ASA-like cyclooxygenase inhibitors with lipoxygenase and/or phospholipase A2 inhibitors partly gave also overadditive antiinflammatory effects in the carrageenin rat paw edema. However, phenylbutazone failed in this respect, possibly due to its different mode of action. Admixture of ascorbic acid rather decreased than increased antiinflammatory activity of cyclooxygenase inhibitors and drug combinations except ASA, the effectivity of which was practically not changed.