This International Standard describes the application of a test using Limulus amebocyte lysate (LAL) reagent for the evaluation of nanomaterials intended for cell-based in vitro biological test systems. The test is suitable for use with nanomaterial samples dispersed in aqueous media, e.g. water, serum or reaction medium, and to such media incubated with nanomaterials for an appropriate duration at 37 °C. This International Standard is restricted to test samples for in vitro systems, but the methods can also be adapted to nanomaterials to be administered to animals by parenteral routes.