In adjuvant-arthritic rats the carrageenin edema of the non-arthritic hind paw was significantly inhibited 24 hours and 3 days after adjuvant injection, but the edema was not influenced at day 14 when the acute phase reaction was still evident and increased anew. Inhibition of the edema in the primary phase may be rather explained by counter-irritation than by the acute phase reaction. No correlation could be found between inhibition of paw swelling and the levels of acute phase reactants after treatment with dexamethasone, indomethacin, aspirin or soybean trypsin inhibitor. It is mainly the secondary phase of adjuvant arthritis which cannot be inhibited by treatment with several proteins. The present results indicate that the acute phase reaction has a negligible modulating influence on the secondary phase of adjuvant arthritis and that consequently the alteration of the acute phase reaction by anti-inflammatory therapy does not seem to disturb a homeostatic mechanism especially regarding the paw swelling.