Increasing anthropogenic pollution of almost all ecosystems and the accompanying negative effects on plants, animals and humans led to extensive monitoring programmes for the continuous surveillance of the environment. An important aspect of the surveillance of the environment is the observation of heavy metal burdening. While some heavy metals, e.g. copper, manganese and zinc - within certain bounds of concentrations - are essential nutrients for plants, others e.g. lead, cadmium, chromium and mercury are toxic even in very small quantities. Besides conventional methods of ambient air monitoring based on physicochemical measurements, alternative methods using organisms as bioindicators for the surveillance of the environment are used more and more often. Because of their anatomical and physiological properties, bryophytes are better suited as bioindicators for heavy metal burdening than most phanerogams. These advantages of using bryophytes for biomonitoring are supported by many authors. There are two fundamental strategies of monitoring in biosurveillance: Passive monitoring: Examination of organisms which occur naturally in the investigation area. Active monitoring: Examination of organisms that were placed into the investigation area according to standardized procedures. The Sphagnum-bag-technique described in this guideline is a method of "active" biomonitoring.