The use of GPS receivers in scientific research, in the implementation of research results or in the completion of environmental tasks defined in certain EU directives, is becoming increasingly important. The measurement technique and receiver operation have been made simple and user-friendly, meaning that research biologists can often take themselves field measurements that in previous years required the skills of a chartered land surveyor. Geometric and descriptive databases updated on a daily basis are indispensable for the efficient operation of GIS/SIP systems that support decisionmaking processes and the implementation of protection programmes in national parks and other environmentally sensitive areas. GPS receivers with the option of logging measurement data are becoming the most popular tool used to update databases in an efficient and affordable way. The need to develop digital maps of protected areas and forested land managed by Regional Forest Enterprises has been emphasised more and more in recent years. In many cases, a DGPS measurement is the only source of information in the process of reviewing existing data (e.g. in the calibration of analogue maps) or measurements of control points on archived aerial photographs. Recent examples of the implementation of GPS technology in environmental research include the development of photo-interpretation models used to obtain remote-sensing pictures (aerial photographs and satellite images), or navigation in training, monitoring and observation areas. A GPS receiver, equipped with a data logging device and software, including a data dictionary, significantly improves the efficiency of field data collection and the transfer of data to geometric and descriptive databases of GIS (SIP) systems. The scope of use of GPS receivers in Polish national parks (NP) varies according to the financial resources available to purchase the receivers, the GIS systems implemented and the adoption of an open approach to geomatics systems. The National Forest Enterprise (PGL Lasy Panstwowe), which manages 25% of the Polish territory, approved the use of GPS receivers in forest management in 2001. The receivers have principally been used to update the Forest Digital Map, i.e. a geometric database. The map viewers and software necessary to update information, introduced recently, enable managers to make use of data obtained from GPS receivers. The receivers may be useful in the operation of forest machinery (forest utilisation) or in protective action (aerial spraying or fire fighting) - these options have also been implemented in the National Forest Enterprise. The use of GPS in navigation significantly reduces expenditure on transport and optimises journeys to monitoring points. In view of the National Afforestation Programme adopted by the Polish government, the use of GPS receivers in navigating and measuring newly forested areas or wood succession in post-agricultural areas takes on a new dimension. Recently, we have observed a growing interest from biologists and personnel employed in national parks or nature reserves in the integration of GPS receivers with data logging devices equipped with LCD displays, i.e. with hand-held computers. The EU programmes, including Phare, have provided significant support for managers applying the GPS technology in areas included in the "Natura 2000" European ecological network. Large-scale use of GPS receivers in protected areas with varying status, and even in the National Forest Enterprise, has its disadvantages resulting from the relatively low accuracy of the devices that are actually used. The consequences of a measuring error in the positioning of a wolf track, even by a dozen metres, may be negligible, but measurements of nature reserve boundaries or the location of an endangered plant species require precision - the use of differential measurements (DGPS) is necessary. Unfortunately, this method is not always available due to receiver features; moreover, some sers are not aware of the Differential GPS method. In most cases, measurements are corrected with the use of data from base-stations (Tatra NP), radio beacons on the Baltic Sea coast (Woliński NP, Słowiński NP), satellite signals or signals from the generally available Active Geodetic Network (ASG-PL), which were used in the tests performed in Miasteczko Śląskie.