This document describes the basis for, selection of, and general applicability of a threshold of toxicological concern (TTC) value for a constituent present in/on a medical device or released from a medical device. The TTC values in this document can be used for: — comparing to a maximum concentration of an identified or unidentified constituent in an extract (see ISO 10993-18); — supporting toxicological equivalence; — comparing to a maximum exposure dose estimate of an identified constituent (see ISO 10993-17). NOTE Constituent is defined in 3.1. ISO 10993-18 specifies how to convert TTC (µg/d) into a concentration (µg/ml). TTC is not applicable to constituents with adequate toxicity data for deriving a tolerable intake (TI) value (see ISO 10993-17). The TTC values established in this document are protective for carcinogens, systemic toxicants, and reproductive toxicants (see Clause 5). This document does not include TTC values for other biological endpoints assessed as part of the biological evaluation of a medical device, per ISO 10993-1, for example: — cytotoxicity; — irritation; — sensitization; — hemocompatibility; — material mediated pyrogenicity; — local effects that occur in tissues at the site of contact between a medical device and the body (e.g. the observations from implantation studies). The TTC values in this document do not apply to potential exposure via gas pathways of medical devices. For application of TTC for constituents present/released from these devices, see the ISO 18562 series. The TTC values presented in this document are not applicable for the safety assessment of cohort of concern (see 5.3).