Aortas removed from rats treated with bacterial endotoxin displayed a reduced sensitivity to calcium (CaCl2, 10 microM-10 mM) in depolarizing medium (100 mM K+). Sensitivity was reduced further in the presence of L-arginine (1 mM) but restored to control by N omega-nitroarginine methyl ester (L-NAME, 300 microM) or NG-monomethyl-L-arginine (L-NMMA, 300 microM), inhibitors of nitric oxide synthesis from L-arginine. Furthermore, addition of methylene blue (10 microM), an inhibitor of soluble guanylate cyclase, restored the contractile response to 10 mM CaCl2. The results suggest that vascular hyposensitivity to calcium involves stimulation of guanylate cyclase subsequent to activation of the L-arginine pathway by endotoxin.