Test guideline development and animal welfare: regulatory acceptance of in vitro studies.

Toxicity studies are necessary in order to be able to identify the potential hazards of chemical interference with human reproduction. Until today, most useful contributions to the assessment of possible human reproductive toxicity are considered to be made by animal studies. The OECD Test Guidelines provide the international standards for safety testing and, consequently, have traditionally focused on animal studies. However, the OECD Member countries consider the welfare of laboratory animals also of importance and are of the opinion that animal welfare considerations should significantly influence the work in the OECD Chemicals Programme. A constant effort is being made to discover alternative testing systems and to achieve their regulatory acceptance. However, activities predominately focus on finding alternatives to existing animal studies, rather than developing nonanimal tests that could contribute significantly to the hazard identification process. An approach based on the selection of endpoints essential for hazard identification that would focus on demonstrating similarities with the "real life" target events is considered likely to achieve regulatory acceptance much earlier than an approach based on high correlations between the alternative method and the existing animal study it is supposed to replace, simply because it is never better than the existing method, but at most "almost as reliable."