One group of subjects will have a clinical history of perennial rhinitis symptoms associated with dust exposure or not associated with other perennial allergens. These subjects will be ppt negative and intradermal skin test positive to Dp. The other group of subjects will be the control group. They will be healthy with no history of rhinitis or rhinitis symptoms. They will be skin test negative. This group will also perform the same nasal challenge with placebo or Dp extract three times daily each for 2 weeks. This group will also perform the same tests as the rhinitis group.