Olfactory cilia preparation from rats contain considerable activity of soluble guanylate cyclase as indicated by the formation of cyclic GMP (cGMP) upon application of nitroprusside, a nitric oxide generating agent. Stimulation of olfactory cilia with high doses of odorants elicited a delayed and sustained elevation of the cGMP-concentration. The odorant-induced cGMP-response was abolished by L-NG-nitro-arginine, a selective inhibitor of nitric oxide synthesis, as well as by haemoglobin which efficiently binds and inactivates nitric oxide. These observations suggest that the NO/cGMP cascade may plan an important role in signal processing of the olfactory system.