Several lines of evidence suggest a regulatory role for the non-adrenergic, non-cholinergic (NANC) nervous system in the airways of the guinea-pig and man. We examined NANC frequency-response characteristics (0.2-90 Hz) with respect to segmental differences and effects of cyclooxygenase-inhibition (indomethacin 10 microM). Furthermore, the neurogenic contribution to the contractile and the relaxatory NANC response was quantified with tetrodotoxin (1-10 microM). Frontally opened guinea-pig airway rings (n = 3-7) were used. NANC responses were obtained by electrical field stimulation (0.5 ms; 1200 mA; 240 s). A relaxatory NANC response was demonstrated in the proximal and the distal trachea. A contractile NANC response was demonstrated in the distal trachea and the main bronchus. Indomethacin lowered the baseline tension, decreased the relaxatory and increased the contractile NANC response (p less than 0.05; at 0.8 Hz; n = 4). A relationship between the baseline tension and the NANC response is suggested. The relaxatory NANC response was tetrodotoxin-sensitive at 3 Hz stimulation frequency (p less than 0.05; n = 3). At this frequency, the contractile NANC response was also mainly tetrodotoxin-sensitive (p less than 0.05; n = 6) whereas at 60 Hz a dominant, tetrodotoxin-resistant contraction was demonstrated. The pronounced frequency-response relationship as well as the tetrodotoxin sensitivity at very low frequencies (0.2-1.6 Hz) indicates that tetrodotoxin-sensitive NANC nerves are stimulated optimally at low impulse frequencies.