The effects of oxymetazoline nose drops on the vascular permeability of the nasal mucosa in a provoked inflammatory reaction was studied in anesthetized rabbits. Vascular permeability (125I-albumin) was 53% higher in the leukotriene B4-provoked nostril (LTB4) compared with the vehicle-treated con-tralateral nostril (p < 0.05). The amount of secretions was, however, not different from the vehicle-treated side. The LTB4-induced increase in permeability was decreased by 22 % when oxymetazoline was introduced (p < 0.05), and the amount of secretions was reduced by 22% (p < 0.01). The effect of oxymetazoline on the vascular permeability of the nasal mucosa can be attributed to a vascular constriction (decrease in blood flow) and/or a change in the permeability characteristics. The LTB4-induced increase in vascular permeability was not attenuated by the monoclonal antibody IB4 directed against the neutrophil adhesion complex CD 11/CD18. The latter suggests that LTB4-induced vascular permeability does not require CD18-mediated neutrophil adherence in the nasal mucosa.