]> Position-Specific Iteration BLAST. Query an amino acid (protein) sequence against a library of amino acid (protein) sequences. More sensetive that BLASTP for detecting distantly related sequences. "Position specific iterative BLAST (PSI-BLAST) refers to a feature of BLAST 2.0 in which a profile (or position specific scoring matrix, PSSM) is constructed (automatically) from a multiple alignment of the highest scoring hits in an initial BLAST search." Source: http://www.ncbi.nlm.nih.gov/Education/BLASTinfo/psi1.html