We stated that SART-stressed guinea pigs showing nasal mucosal hypersensitivity would serve as an animal model for the in vivo evaluation of antiallergic drugs. In the present study, the mode of action of Neurotropin on nasal allergy compared with those of antiallergic drugs was studied by using SART-stressed guinea pigs. Daily administrations of Neurotropin improved the methacholine-induced hypersecretion and histamine-evoked sneeze response, which are parameters of nasal mucosal hypersensitivity, and increased the density of muscarinic ACh receptors located on the nasal mucosa caused by SART stress. In addition, the inhibitory action on nasal secretion in a passively sensitized model was more intense in SART-stressed guinea pigs than in normal ones. Ketotifen and tranilast were also found to have marked effects on nasal secretion in the passively sensitized SART-stressed model, but only had weak effects on nasal mucosal hypersensitivity. Neurotropin significantly potentiated the action of ketotifen or tranilast. Thus, at least part of the inhibitory effect of Neurotropin on nasal symptoms such as watery secretion and sneezing is thought to have been brought forth through the regulatory action on nasal mucosal hypersensitivity, and its combined use with antiallergic drugs would be a very effective therapeutic regimen for nasal allergy.