It is widely considered that it is not appropriate to treat beta-pairs in isolation, since other secondary structural Models (such as helices, coils), protein topology and protein tertiary structures would limit beta-strand pairing. However, to understand the underlying mechanisms of beta-sheet formation, studies ought to be performed separately oil mole concrete aspects. In this study, We FOCUS On the parallel or antiparallel orientation of beta-strands. First, statistical analysis was performed oil the relative frequencies of the interstrand amino acid pairs within parallel and antiparallel beta-strands. Consequently, features Were extracted by singular value decomposition from the statistical results. By using the support vector machine to distinguish the features extracted front the two types of beta-strands, high accuracy was achieved (up to 99.4%). This suggests that the interstrand amino acid pairs play a significant role in determining the parallel or antiparallel orientation of beta-strands. These results May provide useful information for developing Other Useful algorithms to examine to the beta-strand folding pathways, and could eventually lead to protein structure predictions. Crown Copyright (C) 2009 Published by Elsevier Inc. All rights reserved.