The aim of the study was to characterize the mechanism of formaldehyde (FM)-induced nasal and bronchial response in asthmatic subjects with suspected FM allergy. Ten subjects purported to have FM rhinitis and asthma and 10 healthy subjects submitted to an inhalation provocation in an exposure chamber with FM at a dose of 0.5 mg/m3 over 2 hr. Spirometry at rest and following bronchial provocation with histamine (PC20) were recorded before and after FM inhalation. In addition, FM-specific serum IgE antibodies were measured and cellular, biochemical, and mediator changes were assessed in nasal lavage before, and immediately after, provocation and at 4 hr and 24 hr later. Provocation with FM caused only transient symptoms of rhinitis in both groups. None of the subjects supposed to have occupational asthma developed clinical symptoms of bronchial irritation. No specific IgE antibodies to FM were detected in persons with occupational exposure to FM. No differences in the nasal response to FM were found between subjects reporting to have occupational allergic respiratory diseases and healthy subjects (P > 0.05). In summary, inhaled formaldehyde at a level as low as 0.5 mg/m3 did not induce a specific allergic response either in the upper or in the lower part of the respiratory tract. Moreover, there is no difference in nasal response to FM in asthmatic subjects occupationally exposed to FM and healthy subjects.