The study investigates possible implication of nitric oxide and prostanoids into anaphylactic reaction in small mesenteric and coronary arteries. Isolated arteries from guinea pigs, sensitized with 0.5 ml of horse serum or sham sensitized were used; anaphylactic reaction was performed in vitro. Contractile responses of small mesenteric and coronary arteries (normalized diameter -350–450 mm) were recorded in small blood vessels wire myograph. Antigen challenge was followed by peak contraction of the vessels, in 60% of cases followed by second phase contraction. Only the weak and not significant relaxations (p>0.05) before the peak contraction to the antigen were recorded in mesenteric arteries precontracted with phenylephrine (30 mM). Pre-incubation with nitric oxide synthase inhibitor, N(G)-nitro-L-arginine methyl ester (L-NAME; 30 mM) resulted in the significant increase of peak contraction to the antigen in coronary (n=7, (p<0.05)) but not mesenteric (n=5, (p>0.05)) arteries. An inhibitor of cyclooxygenase, indomethacin (10 mM) has significantly (p<0.05) attenuated the peak contraction to the antigen in both types of small blood vessels investigated. In conclusion, the arterial contraction induced by anaphylaxis could be partially attenuated by the endothelium-derived nitric oxide in coronary arteries, but enhanced by the cyclooxygenase products in both coronary and mesenteric small arteries.