Patients with house dust mite allergies frequently exhibit very different symptoms to those allergic to other inhalant allergens. The frequency of comorbid allergic asthma in these patients is increased. Therefore, diagnosing patients with suspected house dust mite allergies can be difficult. It is important to distinguish between sensitization to an allergen and a clinically relevant allergy. Nasal provocation testing (NPT) is a reliable method to identify patients suitable for a causal treatment (specific immunotherapy). Position papers on methodology and interpretation of NPT data are available. Skin prick and allergen-specific IgE tests reveal a reasonable correlation with NPT results, although this is inexact to some extent. Performance of NPT in patients with suspected house dust mite allergy is important in individuals with questionable symptoms and unclear skin and blood test results, particularly prior to initiation of allergen immunotherapy.