A diffusive sampler for NO ₂ , Willems badge, was validated in laboratory experiments and field tests. The collecting reagent for NO ₂ in the sampler is triethanolamine, and the analysis is based on a modified colorimetric method, the Saltzman method. The analysis was performed by a flow injection analysis (FIA) technique. The sampling rate for the sampler was determined to be 40.0 ml min ^–1 . There was no effect of NO ₂ concentration or relative humidity on sampling rate, and the influence of sampling time was found to be small. The detection limit was 4 µg m ^–3 for a 24 h sample. The capacity is high enough to allow sampling of 150 µg m ^–3 for 7 days, which is twice the recommended Swedish short-term (24 h) guideline value as a 98-percentile over 6 months. In field tests, the sampler performed well, even at wind speeds higher than 2 m s ^–1 , and at low temperatures. The overall uncertainty of the method was 24%. The sensitivity and capacity of the method also make it suitable for personal sampling for 2-8 h in working environments.