PSI-BLAST
From BioPerl
PSIBLAST - Position Specific Iterative BLAST - iteratively searches one or more protein databases for sequences similar to one or more protein query sequences. PSIBLAST is similar to BLAST except that it uses position-specific scoring matrices (PSSMs) derived during the search.
The actual PSIBLAST tool is called blastpgp in the NCBI version.
More information in NCBI's PSIBLAST tutorial.
