The purpose of this study was to assess intrinsic smooth muscle mechanisms contributing to greater NO responsiveness in pulmonary vascular versus airway smooth muscle. Porcine pulmonary artery smooth muscle (PASM) and tracheal smooth muscle (TSM) strips were used to perform concentration response studies to the NO-donor, (Z)-1-[N-(2-aminoethyl)-N-(2-ammonioethyl)amino]diazen-1-ium-1,2-diolate (DETA-NO). PASM consistently exhibited greater relaxation at a given [DETA-NO] (NO responsiveness) than TSM (log EC₅₀ -6.55 ± 0.11 and -5.37 ± 0.13 for PASM and TSM, respectively, P < 0.01). The relationship between tissue cGMP ([cGMP]_i) and relaxation was determined using the particulate guanylyl cyclase agonist, atrial natriuretic peptide (ANP). ANP resulted in complete relaxation with no detectable increase in [cGMP]_i in PASM and only 20% relaxation with a 10-fold increase in [cGMP]_i in TSM, indicating that TSM is less cGMP responsive than PASM. cGMP-dependent protein kinase I (cGKI) mRNA expression was greater in PASM than in TSM (2.23 ± 0.36 versus 0.93 ± 0.31 attomoles mRNA/µg total RNA, respectively, P < 0.01), but total cGKI protein expression was not (0.56 ± 0.07 and 0.49 ± 0.04 ng cGKI/µg protein, respectively). The phosphotransferase activity for the soluble fraction of tissue homogenates demonstrated no difference in the cGMP EC₅₀ between PASM and TSM. Phosphotransferase activity indexed to cGKI differed significantly between PASM and TSM (1.61 ± 0.15 and 1.04 ± pmol[[rad]]min^-1[[rad]]ng cGKI^-1, respectively, P < 0.05). An intrinsic smooth muscle mechanism contributing to greater NO responsiveness in PASM versus TSM is greater cGMP responsiveness and increased cGKI specific activity in PASM.