There is an increasing demand for network analysis of protein-protein interactions (PPIs). We introduce a web-based protein interaction network analysis platform (PINA), which integrates PPI data from six databases and provides network construction, filtering, analysis and visualization tools. We demonstrated the advantages of PINA by analyzing two human PPI networks; our results suggested a link between LKB1 and TGFbeta signaling, and revealed possible competitive interactors of p53 and c-Jun.