Local nasal hyperthermia or inhalation of heated water vapor is often recommended as a home remedy for various rhinitis disorders such as the common cold and allergic rhinitis. Inhaled heated vapor treatments and simple saline solution nasal irrigation were investigated for their effect on inflammatory mediator production in nasal secretions. Three treatments were given for nasal irrigation: heated water particles (large particle water vapor) at 43 degrees C, heated molecular water vapor (molecular water vapor) at 41 degrees C, and simple saline solution nasal irrigation. Nasal washes were done before each treatment (baseline), immediately after treatments, and at 30 min, 2, 4, and 6 h. Histamine, prostaglandin D2, and leukotriene C4 (LTC4) concentrations were measured in nasal secretions and compared with baseline values. Thirty symptomatic patients with active perennial allergic rhinitis underwent three treatments at weekly intervals. Nasal histamine concentrations fell substantially with the nasal irrigation (p < 0.01 immediately posttreatment and at 30 min; p < 0.05 at 2, 4, and 6 h). Large particle vapor also reduced histamine concentrations for up to 4 h posttreatment compared with baseline values (p < 0.05). Alternatively, molecular water vapor did not alter nasal histamine concentrations. Surprisingly, the three treatments did not alter prostaglandin D2 concentrations over the 6 h. Leukotriene C4 concentrations fell briefly after the large particle treatment but did not with the molecular water vapor. With saline solution irrigation, LTC4 concentrations in nasal secretions were lower than baseline at 30 min to 4 h after a treatment (p < 0.05). This study demonstrated the usefulness of large particle vapor treatment and saline solution irrigation in reducing inflammatory mediators in nasal secretions and indirectly supports the clinical efficacy of these treatments for chronic rhinitis.