After quick freeze-clamping of tissue segments in liquid nitrogen, we could also measure cyclic nucleotide levels or evaluate adenylyl or guanylyl cyclase activities. It was obvious to us that we should also add these new guanylyl cyclase activators to bovine tracheal smoth muscle segments and evaluate motility and cyclic GMP accumulation. We found that these agents as with other tissues increased cyclic GMP levels as expected and simultaneously caused relaxation n precontracted muscles.