This part of DIN ISO 16000 is a test standard for the area of environmental protection and is intended to be used to characterize indoor air with regard to formaldehyde. The standardized measuring method is important to recognize indoor pollution of relevance to health and may have far-reaching implications as the investigation result can have considerable consequences, for example, with regard to the need for renovation or the success of renovation. In addition to the field of private households, internal spaces according to this standard are offices, schools, nursery schools, hospitals, event locations (such as theatres, cinemas) as well as the cabin interiors of vehicles, amongst others. Formaldehyde has a high potential toxicity. Therefore, its determination is of interest as an indoor air pollutant. Formaldehyde is an irritant that may cause allergic reactions and other health issues. Formaldehyde is used in the production of ureaformaldehyde resins, adhesives and insulating foams. Emissions from particle (chip) board and wall insulation are the major sources of formaldehyde in indoor air. This part of ISO 16000 specifies a method for determination of formaldehyde (HCHO) in air. Formaldehyde is collected in a diffusive collector; during this process a conversion of formaldehyde to the corresponding hydrazone takes place on silica gel papers which have been coated with 2,4-dinitrophenylhydrazine (DNPH). A stable hydrazone is formed which can be desorbed by acetonitrile. The solution is analysed by means of a high performance liquid chromatograph (HPLC) equipped with an ultraviolet (UV) detector. The diffusive sampler may also be used for personal sampling. For this purpose it is attached to the clothing of the person being monitored. The test method is applicable to the measurement of formaldehyde in indoor air over the range from 0,001 mg/m3 to 1,0 mg/m3 for a sampling period of between 24 h and 72 h. For sampling periods of 24 h, the suitable formaldehyde concentration range is 0,003 mg/m3 to 1 mg/m3, and for 72 h it is 0,001 mg/m3 to 0,33 mg/m3. Confirmed samplers with respect to measurement sensitivity and precision can apply to short-term sampling (less than 24 h). The method is suitable for measurements in atmospheres with conventional indoor air relative humidity and for monitoring at air velocities as low as 0,02 m/s. The chromatographic step in the method is designed to eliminate potential interferences, including those due to the presence of other carbonyl compounds. The sampling method gives a time-weighted average result. The document is directed at representatives of supervisory authorities, testing laboratories, professional associations and planning offices as well as representatives of interior designers, furniture industry, paint industry, adhesives industry, automotive industry or other branches producing items for the interior. The International Standard has been prepared by Working Group 2 "Determination of formaldehyde" of ISO/TC 146/SC 6 "Indoor air". The secretariat of SC 6 and the chairmanship are held by Germany. The responsible German committee is NA 134-04-04-01-01 AK "Planung von Innenraumluftmessungen" ("Planning of indoor air measurements").