It has been demonstrated that platelet-activating factor (PAF)-acether can induce nasal neutrophilia and eosinophilia, with a different degree of responsiveness in atopic and in nonatopic subjects. The aim of this study was to evaluate whether PAF can also induce the release of secondary mediators in the human nose. Ten patients with allergic rhinitis and 10 normal subjects underwent nasal challenge with PAF (500 nmol), lyso-PAF (500 nmol) and saline solution. Nasal lavages were performed before and after challenge to evaluate changes in nasal cytology and release of histamine, immunoreactive leukotriene (iLT) C4 and eosinophil cationic protein (ECP). PAF caused neutrophilia and eosinophilia, which appeared earlier in atopic than in nonatopic subjects (30 min vs 1 h), and peaked 3 h after challenge in both groups. Lyso-PAF caused mild neutrophilia, which appeared 3 h after challenge in both groups; an increase in eosinophil counts was observed 3 h after challenge in atopic subjects, but not in nonatopic subjects. PAF insufflation caused a significant release of ECP in nasal lavage fluids 30 min and 3 h after challenge in atopic subjects, and 3 h after challenge in nonatopic subjects. ECP levels in the nasal lavages collected 30 min and 3 h after challenge with PAF were higher in atopic than in nonatopic subjects. Eosinophil counts correlated with ECP levels in the nasal lavages collected 30 min after PAF challenge in atopic subjects. Nasal challenge with lyso-PAF did not provoke any release of ECP. No significant increase of histamine and iLTC4 levels in nasal lavages was found after challenge with either PAF or lyso-PAF.(ABSTRACT TRUNCATED AT 250 WORDS)