Experimentally determined protein structures formed the basis of the CASP7 prediction assessments. These target structures were assigned to one or more tertiary structure prediction categories and where necessary were divided into structural domains. Boundaries for these domains were based on visual inspection of the targets and superpositions of the target with template structures. Target domains were classified into three different categories for assessment: "high accuracy modeling," "template-based modeling," and "free modeling." Assessment categories were determined by structural similarity between the target domain and the nearest structural templates in the PDB and by the accuracy of the models submitted by the predictors or by whether or not template information was used to generate the predictions. In CASP7 108 of the 123 target domains were evaluated in the template-based modeling category and the remaining 15 target domains were classified as free modeling. A total of 28 target domains from the template-based modeling category were also assessed in the high accuracy category and four overlapped with the free modeling category.