Late allergic reactions (LAR) following allergen challenge occur in different compartments. We studied the kinetics of nasal and bronchial nitric oxide (NO) in mild asthmatics after allergen challenge. Twelve males with intermittent asthma (28 yr, FEV1 97% of predicted, PC20methacholine <8 mg/ml) and known LAR after bronchial allergen challenge underwent nasal and bronchial allergen provocation using the same allergen separated by a washout of 3 weeks. Nasal and bronchial NO were measured before challenge, during early (EAR) and late phase reactions, and 24 h after allergen. The mean (sem) maximum fall of FEV1 at EAR was 31.9+/-3.2% (P=0.001), and 17.6+/-2.2% (P=0.004) during LAR. All patients developed nasal EAR (max. fall in nasal rhinomanometric flow 64.8+/-7.6% of baseline) after nasal challenge, and 10 patients demonstrated nasal LAR with a fall in nasal flow of 65.9+/-6.6% (both P=0.002, respectively). During EAR, there was stronger reduction of nasal (-19.2+/-6.2%,P=0.039) than bronchial NO (-6.9+/-5.2% of baseline, P=ns). In contrast, bronchial NO also tended to decrease during bronchial LAR (-8.8+/-6.8%,P=ns), while nasal NO slightly increased non-significantly (+17+/-10.8%, P=ns). After 24 h, bronchial NO was significantly elevated (+78.1+/-40.1%, P=0.039), whereas nasal NO was unchanged (+6.1+/-15.1%, P=ns). The intraindividual difference between bronchial and nasal changes of NO during LAR, but not EAR or after 24 h, was significant (lung vs. nose: -35.6+/-14.1% relative difference, P=0.039). Despite similar functional responses in nose and bronchi, nasal NO kinetics following allergen challenge differ from bronchial NO. The concise mechanisms accounting for this discrepancy warrant further investigations.