In Vitro toxicology methods are being validated and adopted by regulatory agencies for use as alternatives to animal testing. Such methods may use ex vivo tissues or bioconstructs, some of which may be proprietary. Users of the data from these methods need to be reassured that the assays or assay components used in their studies provide consistent, good quality data over time, matching the standards achieved during the validation process. This paper presents an overview of approaches currently used by representatives of a manufacturer and a contract testing laboratory to ensure that the results from in vitro alternative methods are reproducible and of high quality over time. These approaches include full characterization of cells or tissues, sampling of each lot of manufactured bioconstructs for performance, and regular use of controls and benchmark chemicals to provide assurance of consistency of assay performance.