The results of a comparison study of the Palmes tube, the Pro Tek and the Chronotox air monitoring systems for determination of nitrogen-dioxide (10102440) levels in personal air samples were reported. Exposure of the samplers to nitrogen-dioxide was for variable time periods but at constant conditions of temperature, relative humidity, and face velocity. Differences inherent in these three dissimilar pieces of equipment necessitated the use of three different analytical procedures. The Palmes tube had the advantages of being small and light and very economical. However, this instrument required considerable analytical support, and of the systems tested, this was the only one which required chemical separation. The Pro Tek system was almost completely automated and easy to calibrate and read in the field, but quite expensive. The Chronotox system was also expensive but allowed the user to comply with OSHA requirements through the stage of record keeping. This latter system was also easy to use in the field, and had the distinct advantage of documenting peaks of concentration throughout the shift, an important consideration for a compound such as nitrogen-dioxide. At the 0.5 part per million (ppm) level, no monitor could accurately sample a 15 minute run, and only the Palmes tube could accurately sample the 4 and 8 hour runs at this air concentration of nitrogen-dioxide. At the 5ppm level, only the Palmes instrument was capable of measuring a 15 minute exposure, while all three devices could accurately monitor 4 and 8 hour exposures. Both the Pro Tek and Palmes tube monitored accurately for a 15 minute exposure at 10ppm concentration, with the Palmes tube losing precision at the highest level during longer exposure periods.