Work-site chemicals are substances which are employed in manufacturing industrial operations. Contact with such materials may present a hazard to health. Substantial hygienic significance is to be attached to the detection of such injurious potentials by experimental and theoretical toxicology. The preparation of toxicologic expertises on industrial materials presents many problems. The standard approach is to utilize scientific methods on the basis of defined experimental models and quantitative relationships. Judgment of the toxicologic relevance is guided by well-documented epidemiologic or experimental data and the study of case histories. After scientific validation the result is used in practice for setting threshold limit values (MAK's, MIK's) for occupational health purposes.