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We employed the random graph theory approach to analyze the protein-protein interacting database DIP, for six different species (S. cerevisiae, H. pylori, E. coli, H. sapiens, M. musculus and D. melanogaster). Two global topological parameters (node connectivity, average diameter) were used to characterize these protein-protein interaction networks (PINs). The logarithm of the connectivity distribution vs. the logarithm of connectivity plot indicates that it follows a power law behavior quite well for the six species. We also demonstrated that the interaction networks are quite robust when subject to random perturbation. Node degree correlation study supports the earlier results that nodes of low connectivity are correlated, whereas nodes of high connectivity are not directly linked. These results provided some evidence suggesting such correlation relations might be a general feature of the PINs across different species.