Predictive value of animal studies in toxicology.

The three main purposes of experimental toxicology are (1) determination of the toxicological spectrum in selected laboratory animal species; (2) extrapolation to other species and prediction of adverse effects in man; and (3) determination of safe levels of exposure. Toxicology has reached a satisfactory level of performance in identifying toxicity in animals, and experimental techniques are now available to characterize the toxicological potential of chemical substances in great detail. In many instances, extrapolation of toxicological findings in animals to man is possible. It must also be admitted that toxicological studies have, at times, failed to predict human toxicity. In many cases, this can be explained by biological differences between animals and man. A particularly difficult problem is the "low incidence responses" that occur only in especially sensitive individuals. They represent a challenge that can be met only be a determined research effort. Failure to predict toxic responses in man is sometimes also brought about by the toxicologists' own faults. It is essential, therefore, that we analyze the errors committed in the past and continuously evaluate and improve our performance. Society's demand for specific safe levels of exposure is difficult to meet. After a long period of confusion and confrontation, toxicology appears to be on the road to a truly science-based methodology for risk assessment.