It is important to review existing toxicity data of chemicals as well as conduct of toxicity tests.It provides toxicological information on similar class of chemicals,and avoids unnecessary tests.A critical first step is to assemble all of the available information on the chemical.There are many information sources of data on physic-chemical properties or mammalian toxicity(e.g.,human data,in vivo or in vitro studies,in silico outputs).The sources include review docu-ments,databanks / databases,published literature,in house company data,or output from internet search engines.They vary in many aspects,including quality,covering fields,extent of peer review,the time-spans of covered,number of chemicals addressed and the extent of detail.Therefore,the second step is to evaluate data quality including reliability,relevance and adequacy.Most of GLP studies in accordance with standardtest guideline are considered to be reliable and relevant.Expert judgment in a weight of evidence approach will be needed for determination of toxicity of chemicals.The quality and consistency of the data,study design,mechanism or mode of action,dose-effect relationships and biological relevance should be taken into account.Examples of useful information sources and key points of data quality will be presented and discussed. It is important to review existing toxicity data of chemicals as well as conduct of toxicity tests. It provides toxicological information on similar classes of chemicals, and avoids unnecessary tests. A critical first step is to assemble all of the available information on the chemical. are many information sources of data on physic-chemical properties or mammalian toxicity (eg, human data, in vivo or in vitro studies, in silico outputs). The sources include review docu-ments, databanks / databases, published literature, in house company data, or output from internet search engines. They vary in many aspects, including quality, covering fields, extent of peer review, the time-spans of covered, number of chemicals addressed and the extent of detail.Therefore, the second step is to evaluate data quality including reliability, relevance and adequacy. Most of GLP studies in accordance with standardtest guideline are considered to be reliable and relevant .Expert judgment in a weight of evidence approach wi ll be needed for determination of toxicity of chemicals. The quality and consistency of the data, study design, mechanism or mode of action, dose-effect relationships and biological relevance should be taken into account. Samples of useful information sources and key points of data quality will be presented and discussed.