BACKGROUND Local allergic rhinitis (LAR) is characterized by in situ production of specific IgE (sIgE) antibodies and a positive response to a nasal allergen provocation test (NAPT) in the absence of atopy. OBJECTIVE The aim of this study was to investigate the immunological mechanisms involved in the immediate and late responses after nasal exposure to Dermatophagoides pteronyssinus (DP) in patients with LAR. METHODS A total of 40 subjects with LAR to DP were studied and compared with 50 healthy controls. Immediate and late responses to NAPT-DP were assessed using a visual analogue scale of nasal symptoms and acoustic rhinometry. Tryptase, ECP, total and sIgE-DP were measured in the nasal lavage by immunoassay at baseline, 15 min, 1, 6 and 24 h after nasal challenge. RESULTS NAPT-DP was positive in all patients, with significant increases in tryptase (45%), ECP (65%) and sIgE-DP (25%) (P<0.05). Sixty percent of the LAR patients presented an immediate response to NAPT-DP and 40% a dual response. Immediate responders showed a fast release of tryptase with a peak at 15 min after NAPT-DP, and a progressive increase in nasal ECP and sIgE-DP from 1 to 24 h after challenge, with a peak at 24 h. Dual responders presented persistently higher levels of tryptase from 15 min to 6 h after challenge, and a similar pattern of nasal release of ECP and sIgE-DP to immediate responders. There were no isolated late responders. NAPT-DP was negative in all healthy controls, with no increases in tryptase, ECP, or total and sIgE-DP in nasal secretions. CONCLUSIONS The results demonstrated the existence of immediate and dual responses to a NAPT with DP in LAR patients, with the local presence of sIgE and mast cell/eosinophil activation.