To investigate the expression levels of three Dsb protein genes,dsbB,dsbD and dsbG,at different time points post C.trachomatis infection,mouse fibroblast 12 cells were chosen to be infected with C.trachomatis serovar F strain F/IC-Cal-13.C.trachomatis elementary body(EB)-infected 12 cells were harvested immediately after EB attachment onto the cells and every 4 hours post infection(hpi) till 44 hpi for total RNA preparation.RT-PCR assays were then employed to amplify cDNA with primer pairs which are specific to C.trachomatis dsb genes dsbB,dsbD,dsbG and tufA respectively.The rela- tive expression levels of Dsb protein genes were evaluated as cDNA ratios of gene dsb to gene tufA.Our results showed that the transcription of dsbG started from 12 hpi and gradually increased till 44 hpi.The transcription of dsbB and dsbD were detected at 16 hpi and reached their peaks at 28 hpi and 24-28 hpi, respectively.Moreover,there was obvious transcription of dsbB at the later stage(44 hpi),but none for dsbD at this time point.We came to the conclusion that the expression levels of the three Dsb protein genes are different during the developmental cycle of C.trachomatist.They may play a role in mid-to-late stage of the developmental cycle of C.trachomatis. To investigate the expression levels of three Dsb protein genes, dsbB, dsbD and dsbG, at different time points post C. trachomatis infection, mouse fibroblast 12 cells were chosen to be infected with C. trachomatis serovar F strain F / IC-Cal-13 .C. trachomatis elementary body (EB) -infected 12 cells were harvested immediately after EB attachment onto the cells and every 4 hours post infection (hpi) till 44 hpi for total RNA preparation. RT-PCR assays were then employed to amplify cDNA with primer pairs which are specific to C. trachomatis dsb genes dsbB, dsbD, dsbG and tufA respectively. The rela- tive expression levels of Dsb protein genes were evaluated as cDNA ratios of gene dsb to gene tufA. Our results showed that the transcription of dsbG started from 12 hpi and increased increased till 44 hpi. The transcription of dsbB and dsbD were detected at 16 hpi and reached their peaks at 28 hpi and 24-28 hpi, respectively. Moreover, there was obvious transcription of dsbB at the later stage ( 44 hpi), but none f or dsbD at this time point. We came to the conclusion that the expression levels of the three Dsb protein genes are different during the developmental cycle of C. trachomatist. they may play a role in mid-to-late stage of the developmental cycle of C.trachomatis.