Bradykinin (BK) and Tyr8-BK induced graded rat paw edema with EC50values of 1.9 and 1.1 nmol/paw, while des-Arg9-BK (DABK, up to 300 nmol/paw) was marginally effective. Tyr8-BK, but not DABK, also caused a dose-related increase in mouse paw edema, with an EC50of 1.3 nmol/paw. The response to Tyr8-BK (10 nmol/paw) in rat paw edema was antagonized by B2receptor antagonists (HOE-140 or NPC 17731, 30 nmol/paw) but not by the B1antagonist des-Arg9[Leu8]BK (DALBK, 100 nmol/paw). Daily intraplantar injections of Tyr8-BK (10 nmol/paw) for 7 days caused progressive desensitization (D) of edema in sham-operated and adrenalectomized Wistar rats. DABK (100 nmol/paw) caused marked paw edema in D paws from both groups, which was inhibited by DALBK (100 nmol/paw) and by dexamethasone (0.5 mg/kg, s.c). Systemic injection of lipopolysaccharide (10 μg/mouse, 24 h prior) potentiated the first and second phases of Formalin-induced pain but had no effect on paw edema. Coinjection of DABK (2–22 nmol/paw) with low doses of Formalin in lipopolysaccharide-treated mice, which had no effect on naive animals, dose dependently potentiated both phases of Formalin-induced pain but did not modify paw edema. These effects were antagonized by DALBK with ID50values of 21.9 (first phase) and 64.1 (second phase) nmol/paw. Thus, both progressive desensitization of B2receptors and systemic treatment with lipopolysaccharide induce a glucocorticoid-sensitive upregulation of B1receptors mediating paw edema in the rat and Formalin-induced nociception in mice. These results suggest that induction of upregulation of B1receptors may play important roles in controlling inflammatory processes and hyperalgesia.Key words: paw edema, rat, mouse, pain, Formalin test, bradykinin, B1and B2agonists and antagonists, lipopolysaccharide, dexamethasone.