Gnarus Systems, Inc. offers cat-SAR, a peer-reviewed computational SAR or in silico toxicity analysis and prediction expert system. cat-SAR is a reliable and cost effective means to predict a range of toxicological or pharmacological endpoints. In simple terms, users send a chemical structure to Gnarus using standard file formats from which cat-SAR makes a prediction and Gnarus returns the result to the user. cat-SAR is completely open with every detail of modeling transparent to the user. Gnarus doesnt employ black box technology. The cat-SAR approach allows the user to select and/or adjust many parameters during the model process from learning set makeup, to selection of types of fragment attributes to consider, to ultimately what numerical or statistical considerations are employed in developing the final model. The cat-SAR approach is also a very dataand informationintensive SAR expert system. During model development and the creation of the final model, all fragments associated with the categories are presented. This leaves the user with an unbiased view of all important features associated with the biological endpoint.