The local lymph node assay: status of validation.

For the prediction of skin sensitization potential of substances, the local lymph node assay (LLNA) is an alternative to the widely used guinea pig tests. Over a 10-yr period this method has undergone extensive development, evaluation and validation. In this commentary, the quality of this validation is examined. It is concluded that the LLNA has successfully passed through all reasonable validation stages. It provides a reliable and relevant source of predictive skin sensitization data which, unlike results from guinea pig tests, are reproducible from laboratory to laboratory. Thus, it is now ready for acceptance as a viable and complete alternative to traditional methods, offering substantial opportunities for reduction in animal usage and improved animal welfare without compromising standards for the identification of significant skin sensitizers.