The measurement of exhaled nitric oxide (eNO) is a non-invasive biomarker of bronchial inflammation. Despite the usefulness of eNO measurement, NO analyzers are too expensive for widespread use by general practitioners. In comparison, the off-line (bag collection) method of eNO measurement may be more useful. In Japan, however, there have been few studies about eNO in asthmatics using the off-line method. This study shows methodological aspects of the off-line method. Briefly, with a SIEVERS bag collection kit, we recommend that the flow rate and pressure level of exhaled air should be 70 ml/sec and 10 cm H2O, respectively and that the sampled air should be measured within 12 hours.