With use of bioinformatics analysis,five completely sequenced L.delbrueckii subsp.bulgaricus and S.thermophilus genomes were scanned in order to predict two component systems(TCSs) and reveal protocooperation between L.delbrueckii subsp.bulgaricus and S.thermophilus.5-9 pairs of the putative TCSs were detected and analyzed in the five genomes.Biological functions of the putative TCSs were predicted by comparing them with those of other microorganisms.Some of TCSs were putatively involved in production of antimicrobial peptides,proteolytic ability,and developing competence etc.The results clue to that the cooperation between L.delbrueckii subsp.bulgaricus and S.thermophilus was established by means of these TCSs.