This document describes the introduction of the concept of property in the field of clinical and environmental human toxicology for the presentation of results of clinical laboratory investigations. It follows the IFCC-IUPAC systematic terminological rules and attempts to create a common base for communication between the clinical chemist, the medical practitioner, the human toxicologist, and the environmental toxicologist. The term designating a substance being a toxicant may be an international nonproprietary name (INN), a generic name, a registered trade name, a fantasy name, or other. This causes difficulties in the transmission of requests and reports on properties involving such substances in biological fluids and environmental media to and from laboratories, to the end user, and in the collating of this information from different sources. The document comprises a list of properties of human and environmental systems involving toxicants for use in transmitting medical laboratory data. The document recommends terms based on the format developed by the IFCC and IUPAC to facilitate interaction between disciplines and unambiguous interpretation of data, e.g. for purposes of risk interpretation. Systematic terms are presented together with a code (identified by the letters NPU) for each. The complete C-NPU Database may be found at: http://dior.imt.liu.se/C-NPU.