We investigated whether the glutamergic system plays a role in isolated trachea from control and ovalbumin-sensitized guinea-pigs. Electrical field stimulation induced contractile responses in control group, but electrical field stimulation produced relaxation responses in ovalbumin-challenged guinea-pigs. The responses induced by electrical field stimulation in both groups were completely abolished by tetrodotoxin, but unaffected by hexamethonium. DL-2-amino-5-phosphono-valeric acid (D-AP5) caused a concentration-dependent statistically significant inhibition in the contractile responses to electrical field stimulation50 (EFS50) in control guinea-pigs. But in the ovalbumin-challenged groups, D-AP5 did not cause any significant effect on the relaxation response to frequency of field stimulation (EFS50). N(G)-monmethyl-L-argine caused a significant inhibition in the relaxation effect of EFS50. L- and D-glutamate and N-methyl-D-aspartic acid (NMDA) alone had no effect on the resting tension on the trachea in both groups. Carbachol produced concentration-dependent contractile responses in ovalbumin-challenged groups. These results suggested that responses to electrical field stimulation in control groups might be due to NMDA receptor-mediated release of any substance on prejunctional neurones and, alternatively, NMDA might exert a modulatory effect on any substance at prejunctional level. Also, responses to electrical field stimulation in ovalbumin-challenged guinea-pigs might not be mediated by NMDA but rather by increasing the production of nitric oxide by inducible nitric oxide synthase.