Nuclear receptors are key transcription factors that regulate crucial gene networks responsible for cell growth, differentiation, and homeostasis. Nuclear receptors form a superfamily of phylogenetically related proteins and control functions associated with major diseases (e.g. diabetes, osteoporosis, and cancer). In this study, a novel method has been developed for classifying the subfamilies of nuclear receptors. The classification was achieved on the basis of amino acid and dipeptide composition from a sequence of receptors using support vector machines. The training and testing was done on a non-redundant data set of 282 proteins obtained from the NucleaRDB data base (1). The performance of all classifiers was evaluated using a 5-fold cross validation test. In the 5-fold cross-validation, the data set was randomly partitioned into five equal sets and evaluated five times on each distinct set while keeping the remaining four sets for training. It was found that different subfamilies of nuclear receptors were quite closely correlated in terms of amino acid composition as well as dipeptide composition. The overall accuracy of amino acid composition-based and dipeptide compositionbased classifiers were 82.6 and 97.5%, respectively. Therefore, our results prove that different subfamilies of nuclear receptors are predictable with considerable accuracy using amino acid or dipeptide composition. Furthermore, based on above approach, an online web service, NRpred, was developed, which is available at www.imtech.res.in/raghava/nrpred.The availability of sequence data for different genomes in recent years has increased the demand for computational tools that can recognize new proteins from this data. The recognition of nuclear receptors is crucial, because many of them are potential drug targets for developing therapeutic strategies for diseases like breast cancer and diabetes (2). Nuclear receptors are one of the most abundant classes of transcriptional regulators, which regulate diverse functions during reproduction, metabolism, and development. Nuclear receptors function as ligand-activated transcriptional factors, providing a direct link between the signaling molecules that control these processes and transcriptional responses (3). The nuclear receptors share a common structural organization. All nuclear receptors consist of six distinct regions or domains as follows: highly variable N-terminal and C-terminal regions (A/B and F domains) that contain one or more transactivation regions; a central, well conserved DNA binding domain (C); a non-conserved hinge region (D) that contains a nuclear localization signal (NLS), and a moderately conserved ligand binding domain (E) (4). The DNA binding domain (C region) of nuclear receptors consists of two zinc fingers, which act as a signature for this superfamily (5). The presence of these zinc fingers facilitates the recognition of nuclear receptors from a genome sequence using simple similarity-based search tools like BLAST and FASTA (6 -7). On the other hand, the major li...